BIOS problem with Aspire 5100

Guys i have a critical situation :
2 Aspire 5100 Notebooks
The first one is mine and has no problems,but the 2nd one wont load neither install any windows system(It freezes on the loading screen) except Vista…
I’ve changed the 2laptops HDDs and mine one worked perfectly but the other one didn’t load windows again so the problem is not in the HDD.
I flashed the laptop with the latest BIOS but nothing changed…
Please tell me what to do…i suppose it is some kind of virus that blocks Windows 9x and NT that stays somewhere out of the Hard Disk.