Odd Windows crashing issues on Dell laptop

I posted here a few months back about my girlfriend's laptop (Dell Inspiron 600M) that she stupidly spilt iced tea on. It had issues where it'd shut off soon after being turned on, so we figured it was fried and needed major rennovations. Basically we got a new motherboard\laptop base on eBay, and put in the old optical drive, hard drive, CPU and screen, all of which seemingly survived the spill.

So after doing all this, Windows happily started up again, but the system would freeze a minute or so after Windows had booted - still image on screen, input devices unresponsive. Bizarrely, rebooting into safe mode was absolutely fine - stable, no issues.

Figured it might have just been Windows getting upset at all the new hardware, so we got a pirated XP SP2 ISO and installed it, but amazingly the damn thing freezes after the formatting step and in the GUI part, at the stage where it's supposedly preparing everything before the installation.

Any ideas on how to fix this? Next step will be the Dell install CD and diagnostics discs, but I'm not confident those will make it work. Is overheating a possibility, or does this sound characteristic of some particular problem that passed my mind? The fact it worked in safe mode for hours confuses things a lot. Oh, and so does the fact that after repeatedly trying to install Windows on it and having it freeze, it chose to not turn on for half an hour or so afterward.

By the way - this is for a girl, so Ubuntu and your other hyper nerdy 1970s command line shit doesn't apply except as a temporary troubleshooting measure. Thank you.

Well, I plan to sell the laptop before the end of the year, and I'm guessing that I'd lose $150-200 of the value if I pulled it apart and sold it as parts, or if I specified that it can't run Windows because of an unknown hardware problem. I'd prefer to avoid that.

So yeah, because I don't want to have to write a thousand words of ad copy on the eBay page extolling the virtues of Ubuntu and how it makes Windows XP irrelevant, I need XP to run on it. And for what it's worth, I don't even know if Ubuntu or any other Linux will boot on it without freezing - do you think that would be a good step towards determining the problem, and how could I use it?