PC connects to internet but can't browse

[badinternet]

a few months ago i moved into an apartment with included internet. i brought my computer that i was using at my last place (where i was paying for my own DSL internet connection) to my new place which has cable internet. i get my connection from my landlords upstairs from their router. as soon as i moved in i was having problems with my internet randomly cutting out for a few seconds and then reconnecting. i told the landlords about this and they said they were having the same problem, so they called SHAW (their service provider) and got a new modem. this seemed to fix the problem for a while. then my internet started cutting out again about a month later. but this time it seemed to be cutting out only if i was downloading a file. then one day my internet just wouldn't let me browse. it would say i'm connected but i can't load any page or update anything. then i find out that if my internet connection is run from the upstairs router into my downstairs router and then into my PC, my internet will work. but if i bypass my router downstairs and run the internet straight from my landlords router upstairs into my computer then my internet doesn't work (it can connect but won't let me do anything with it) i haven't installed any new programs lately but i have noticed one annoying thing. i have my "microsoft protection" or whatever it is on high (it's the thing that causes the popups in the bottom-right corner to warn you about programs trying to change registry entries or open .exe files). and usually it would pop up for safe things i would just click the "always allow" button and it wouldn't pop up again when i was trying to open the same program. but lately (almost around the same time as my recent internet problem) it keeps popping up for everything even though i click the "always allow" button every time i see the pop up. it's like my computer can't remember anything. if anyone has any idea about what might be wrong with my computer could they help me out (oh yeah, and i the problem IS my computer, because right i can use my girlfriend's laptop while running the internet either through my router or straight from upstairs with no problems). any help would be very much appreciated. thanks.