|" It's not a BIOS problem. "|
Your computer may not boot if the ram has a poor connection in it's slot.
See response 2 in this - try cleaning the contacts on the ram modules, and making sure the modules are properly seated:
Installing the wrong ram MAY damage the ram you tried, but it will NOT harm the computer,
UNLESS the ram was installed backwards in the ram slot and you then attempted to boot the computer, in which case both the backwards ram module and the ram slot it is in were instantly fried and neither can ever be used again. In that case, usually the mboard WILL NOT BOOT.
You would probably have noticed a distinct smell like that of burning plastic,and possibly a puff of smoke. There will be at least one damaged or missing contact (it was vaporized or it got so hot it fell off) on the module that was backwards, and damage - melted plastic - or a black carbon deposit -in the ram slot at the same location where the module was backwards.
If you see damage like that, if you use good lighting and cleanup up the damaged ram slot to remove any black carbon deposits or plastic that has melted and is touching a contact, and make sure there is nothing in the slot such as a contact that fell off the module, then the mboard MAY work fine if you install undamaged ram in undamaged ram slots.