I'm sorry no one else has replied to your posting.
I looked at what all you did, and tried with this laptop.
{I don't like working on laptops, I'm more a Desktop PC guy.}
When working on the Laptop MotherBoard.
Did you make sure you were grounded, and had it sitting on a Anti-Static Mat?
You said it was over heating.
Even though you cleaned and re-seated the heatsink assembly.
It could of already been too late, and the damage to the GPU & CPU was done.
Also, you tried to update the BIO's with one that was not made for this Laptop.
You should never need to update the BIO's, unless it is recommended by the MotherBoard Manufacturer.
At this point,
I'd say find another Dell E-Machine of the same model that has been physically damaged.
{Case Cracked, Screen Broken, Keyboard trashed, Dead CD-Rom, Hard Drive or bad Battery Pack.}
Then use this current Laptop as a donor parts machine too repair the other one you picked up.
Sorry, that's about the best I can offer you.
Signed: Ensign Tzap