Unable to set up a network connection

[zaleukos]

I have problems with network connections on one of my two desktops and cant get it to function properly of a LAN or when directly connected to an old ADSL modem. The other machine connects to the modem just fine, so I'm fairly confident the problem isnt with the TP cable nor the modem. The gizmos available are:

1 healthy PC (onboard LAN)
1 ADSL modem (Zyxel
1 problem PC (onboard LAN + old 10Mb Realtek card)
crosswired CAT5 cable.

EDIT: I can either connect the two PCs to each other or connect one PC at a time to the modem. There is no router, no sharing of connections or such, just direct connections between two units through the crosswired TP cable.

Both PCs run Win XP SP2. Everything worked nicely about a week ago (a TCP/IPC LAN for gaming and direct connection of either PC to the modem for surfing) and had done so for a year (or three in the case of the pPC).

I've tried the following:

Switching off firewalls (Kerio on one of them, Sygate Personal Firewall on the other, and of course the Windows XP firewall which has a tendency to switch itself on when changing certain settings).

Switching off AV (Kaspersky)

Switching off the onboard network adapter in the BIOS and putting in an old Realtek card that should work.

Setting static IP in windows (192.168.0.1 and .2 respectively) for LAN and modem connection (though the latter is supposed to do well with dynamically selected IP).

Setting all network adapters to the 10MB half duplex (which should be the slowest transfer rate available).

The results are mixed but generally discouraging:

- Automatic asssignment of IP when connecting to the modem fails. Setting the IP tells gives me the message that I am connected, but I cant ping the modem nor access the config page of the modem from the problem PC.

- I cant ping PC to PC with any of the tested settings.

- The healthy PC is able to set the correct transfer rate if I put the old network adapter in the problem PC.

- Manually setting the same IP for both PCs (or for problem-PC and modem) give me an error message (conflicting IP) on the problem-PC, but not on the healthy PC.

The last issue makes me wonder if communication might be blocked in one direction, but I dont know why as I've switched off all firewalls and cant find any strange residual processes.

For what its worth we had some odd behaviour from the Kerio firewall on the problem PC when these troubles started, which is why we reverted to obsolete Sygate on that machine.

[degsy]

Welcome :)

Does the modem have an IP or config page?

What is it's IP? If it is a router then you will need your PCs to be in the range
e.g. If it's 192.168.0.1 then the PCs will need to be between 2 and 255

What happens if you choose automatically detect when connect directly to the modem?
Do you get a LAN IP or WAN IP?

[zaleukos]

Welcome :)

Does the modem have an IP or config page?

What is it's IP? If it is a router then you will need your PCs to be in the range
e.g. If it's 192.168.0.1 then the PCs will need to be between 2 and 255

Thanks for the greeting:) The modem's config page is 192.168.2.1, which I also set as default gateway when manually choosing IP. My old troubleshooting list that I got for the modem recommends me setting the PCs IP to 192.168.2.2 if I have problems with "limited connectivity".

What happens if you choose automatically detect when connect directly to the modem?
Do you get a LAN IP or WAN IP?

I get a "limited or no connectivity" message and a 169.xxx IP. The healthy PC sets it's IP to 192.168.2.2 when using auto-detect.

[degsy]

Have you tried resetting the modem/router?

Have you tried accessing without the healthy PC connected?

[zaleukos]

Have you tried resetting the modem/router?

No, I havent tried resetting the modem as I thought the problem is with software (or possibly the network adapter, but I've come to doubt that after trying the old realtek adapter), and I dont have any problems with the modem connected to the healthy PC that I am using to post here:) I'd rather avoid resetting it before I've found the configuration details

Have you tried accessing without the healthy PC connected?

This is always the case when the modem is involved. I dont have a router and can only connect one PC to the modem at a time, alternatively connect the two PCs to each other.

I've mainly been trying to get a connection between the two PCs to work or tried to connect to the modem while it was physically disconnected from the outside world. I've used the healthy machine as a reference of how things "should be", as it should have the same windows configuration (they run the same software except for the firewall, and I disable the firewalls while testing).

- Manually setting the same IP for both PCs (or for problem-PC and modem) give me an error message (conflicting IP) on the problem-PC, but not on the healthy PC.

I found this symptom most interesting (the behaviour is for direct connections either to the healthy PC or the modem) as it indicates that communication works at some level. Otherwise all my tests give the negative "it doesnt work" result:(

[degsy]

There are some possibilities to determine a software problem.

Boot into a live CD such as Knoppix or BartPE.
You could even try safemode with networking.

If it still doesn't work, then try resetting the modem, just in case.

If it still doesn't work then it is most probably a hardware problem.

bwt, you have checked the cable used is working?

[zaleukos]

The network cable works, I'm using it now.:)

Thanks for pointing to safe mode, I should kick myself for not trying that, but it gave some info:) Given that the old realtek card works in safe mode and the integrated one doesnt it seems seems likely that the integrated adapter is defective AND that there are software issues...

Btw, windows gives me a "limited connextivity" error in safe mode even when the connection works (I tried pings PC to PC, ping PC to modem, and could access the modems config page using the old adapter). Is that kind of behaviour known?

[degsy]

It may be the settings of the adaptor.
Goto it's properties and try tweaking the Duplex settings.

[zaleukos]

I've tried that already, since the now seemingly faulty network adapter only ever managed to connect to the modem using 10Mb (half duplex).

Given that I have one working adapter I think it will be faster to simply do a reinstall on that machine than to continue troubleshooting. 10Mb is sufficient for our networking needs at the moment.

[zaleukos]

Thought it would be good form to pop in here and mention that the problem was solved this weekend:) It turned out that the on-board adapter is broken and there was a conflict between recent versions of Kaspersky AV and the firewall. Kaspersky is a good AV software but very intrusive, so I guess I'll consider upgrading to Kaspersky Internet Security when the license is up for renewal next year.

Many thanks for reminding me of failsafe mode, without that move I'd never managed to pinpoint the problem:)

[degsy]

Thanks for the update :)