Recently I had a Presario SR1720NX thrown at me for a repair. Nomatter
how many times I reloaded from the restore partition, it would soon lockup after login. Task manager would not work, clicking the mouse did nothing.
It was like the machine would seize up for no reason, as if you had a bad motherboard or something.
I fixed it by reloading with a known good CD of Windows XP Pro. The machine worked fine after that. The fctory image was garbage.
During this time, I also was able to upgrade the Socket 939 Sempron to an Athlon X2 processor (the board will support up to Athlon x2 4800+). No issues were found, swapped out old IDE for a SATA drive as well.