I know a little more than the average person about PCs.
However, I don't know what your level of expertise is in order to do any of the following.

Frankly, it's really hard to say what's causing your system to freeze.
My first question would be have you installed any software or peripheral just before the problem started?
If you did, I'd uninstall whatever you loaded and see what happens

It certainly could be a hardware thing.
The power supply could be it, it could also be that your CPU is overheating.
If you haven't done so already, try opening up your computer's case and spraying out the dust with one of those spray dusters - pay particular attention around the fans and the CPU area.

Make sure you have all the XP updates from Microsoft - Run Windows Update and chose custom update and install any optional updates especially if there any any new drivers for any of your components.
(In a very rare case, sometimes an update can cause the problem and if your system is set for "automatic updates" it's possible that an update caused the problem in the first place - but this is rare).

If all else fails - and I mean if you've even consulted other people and applied their suggestions.
and especially if the only thing you're running on that machine is a label program, reformatting the hard drive and re-installing the operating system and all the Windows Updates not only usually solves the problem, but perks up your computer and makes it as zippy as the day you bought it.
Of course, you'll need all the appropriate disks to reload XP and any programs etc. You'll also need a lot of patience!

Good Luck - I hope I gave you some ideas