laptop freezing

[mosta]

two or three weeks ago, I think, my laptop (ibm thinkpad a31p, win xp pro, sp 2, pentium 4m (I think; not pentium M) started failing to complete the shut down process. I get the screen "windows is shutting" down and it's stuck there. about three days ago the laptop started freezing up while I was using it. I've just pieced together that it seems to happen while I'm typing more than a few words of text. specifically it's frozen repeatedly while working on a word doc, while typing a post on 2+2, and while typing an email in yahoo web mail. I do type some short emails and type url's and other miscellany without freezing. I also played poker for a few hours without freezing (and there was a little typing involved in that). I tried using my backup clone hard drive to boot from, which was cloned after the problem started and had the same problem. then I went back to a system restore point, and went 2 weeks back to try to be before whatever happened. didn't solve it.

what now? does this sound like a software or a hardware problem? I can reformat my HD and reinstall win xp from the ibm hidden partition. I guess I might should just do it now since I don't really have other options.

any guidance or advice? (also, the machine was manufactured in around 2001, but was unsold or unopened so IBM "recertifed" it "as new" and I bought it just over a year ago. I've installed some random software, some of which maybe I should have been more cautious about, but not all that much. i tried uninstalling all but the bare bones, including zonealarm firewall, antivir free anti-virus, process guard, weatherbug, maybe a couple more, and that didn't fix it.)