Well,, what I can tell you is this... first and foremost,, it's an eMachine, yes that is an answer
Second,,, check with eMachine to see if you need a BIOS update.
Third,, if this also happens with Vista, then it is most likely a Hardware problem that eMachine will need to fix
This may be fixed by a BIOS update.
The problem with Vista Ready machines as that not all of them really were vista ready. They got Vista to boot on it and were granted the right to slap a sticker on it saying as much. but not really Vista Ready, I blame both MS and the OEM (eMachine in this case) for this fiasco.
My advice is contact eMachine for assistance, or slap XP back on it and buy a new PC (that is not an eMachine).