Sony Vaio Hungup on the bio screen

Unplug the mains power; remove the battery and hold down the power button for 30 seconds.

If problem persists…. unplug the mains power, remove the battery. Now locate the sdram memory location, it might be under the case, nearby the battery. Undo the cover screws, if there is two memory cards is installed. Remove the one in slot 2. (Remember to touch some metal to discharge yourself from statics, before touching any parts).

Put the battery back on.
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if it still hangs. Repeat above process… Remove the memory in slot 1 and replace it with the other memory card.

If problem persists, try to run memtest+. http://www.memtest.org/

^^Great post above. Sounds like a bad memory stick. With some trial and error, the above should help you find which one it is. If not, then does your battery charge light come on? Have you been having battery issues? Inspect the plug where the power adapter goes into the board and make sure it's not damaged.

Tried the memory of another working machine and its not that. Also the battery is fine. it still hangs on the bio screen. i tried the hardrive in another machine as well so i know it is working. can it be a virus that intercepted the bios? is there a bios override option for sony? Any other ideas?

I would look for a loose connection from the main board to the keyboard. Did you try to boot with no RAM installed? Should still be able to get to the BIOS.
Maybe faulty vRam? Not sure about virus, I suppose it's possible, probably rare. Is cracking open the case and inspecting it an option?

booted with no ram and the problem persist. openned the machine and nothing looked out of place.

got a blue screen "bios on this system is not fully ACPI complaint, visist = www.hardware-update.com". the website doesnt seem like a system that is maintaned. just strange!