When GUI applications fail to respond, one suspect is memory failure. If buttons are unresponsive it could be that the application is trying to run in bad memory. This is something that can happen on old or new hardware. The laptop I'm writing this on had to have its memory replaced when new. The engineer call out probably wiped out the profit margin for the sale. In fact the company went bankrupt soon after, so maybe my machine tipped them over the edge...
I came across it again recently on an old machine. An application GUI was failing to respond. The machine was dual booted with an old version of Ubuntu, with Memtest86+ as a boot option, so I gave it a go.
Memteast86+ is also available as a bootable CD image. The thing to remember is that the program will make multiple passes (i.e. run forever) if allowed. One pass was enough to reveal that something was wrong with this computer.
Luckily it was the smaller of the computer's 1G and 512MB memory cards that had failed, and pulling that out fixed the memory problem, 1G being enough for XP.