Bonjour, je possède un Acer Extensa 4420  
Carte mère AMD Athlon 64 x2 dual-core processor tk-57
 
Here my problem,  
Sometimes my computer don't start, it just don't show any signs of boot screen.
Sometime it works fine and go on Vista well.
 
I was thinking about a virus, but every scan is clear, I tried a lot of antivirus program.  
So I decided to format and install another Windows.  
The problem is that my bios wont accept to save anything.  
So I can't boot on my cd anymore. I tried to FLASH my bios.... it worked well. But unfortunatly it didn't fix my bug.  
 
What do you think it could be?
Thank you for your Help.