Standard "AA" cells don't provide enough current for that! You need "D" cells at least, or a higher-current chemistry like NiMh.
Edit: If by "It's in my PC," you mean you have not felt able to check the PSU (e.g. if opening the case voids a warrantee), then provide the full model name/number of the PC; an online reference will detail what's inside.
The 945 chipset is sufficiently old that any number of things could have happened to this machine. Google "bad capacitors" for what I'd consider a prime suspect this early in the investigation.