I have a custom PC that I built about 6 or 7 years ago that is FREEZING randomly for about 5 now. It is a P4 2.4GHz, has 256Mb RAM, a Mach Speed P4XFCP mother board, G-Force 4 MX440SE graphics card, Western Digital 80gig hard drive, V-Stream VS-L883D video capture card, Generic 3.5in floppy drive, & Lite-on CD burner. I have re-formated with Win XP (format, deleted partition, repartition, & install) 5 times, removed all unnecessary hardware (video capture card & 3.5 drive), swapped with new hardware ( RAM, processor, CD-ROM, & video card). After all that it still freezes at anytime. It may FREEZE at boot or it may freeze after 1 hour of use. There is no consistency. I have tried to run diagnostic software but it could freeze at anytime. If anybody has any ideas of what I could try next it would be good. I think that I have swapped everything but the mother board. All hardware that I swapped with was working. Is there any way it could be the power supply? Thanks for any help. 256 is on the low end for XP RAM...RAM is cheap right now so i'd add at least another 512...if the freezes continue swap in a known working PSU of the same or greater wattage to test if that's the culprit.
But i suspect RAM.Before it started freezing it was running fine. I had not added anything new. It just started freezing. When I swapped the RAM I put a 512 stick in and it was still freezing. When it freezes it just stops responding. The mouse does not move & the keyboard will not work. I have been told that the power supply very rarely has problems. I guess I could try that.I'm confused...you stated you have 256M of RAM...nothing was said about adding 512.
Is the new RAM the correct type ? ?
To check this visit Crucial.com and run a report.

How clean was it inside there when you opened the case ? ?
I still suspect the RAM though.To troubleshoot the hardware I tried swapping the hardware 1 by 1. I made sure the hardware that I put in was correct before I put it in. After I tried the new hardware I removed it and put the original back. As far as the dust on the inside the CPU case has a filter that helps with the dust. I still clean it out with compressed air about every 2 to 3 months.So how much RAM is in there now and are you sure it's the correct type ? ?256 and checked 4 times it ran on this RAM fine for 2 or 3 years. I know I need to get more but I am on a very limited budget and I see no reason to get more for a computer that is not working right now.DDr266 which is what it takes is 20 bucks for a 512M stick...
XP needs more than 256 to run properly.
But that's certainly up to you.

Also the 256 stick may have gone bad...you can DLoad and run MemTest to see if this is the case. If the RAM was bad wiuld replacing it with double what I had not fix it? I was thinking that if the new stick of 512 was going to work I would have left it in and be done but, it did not fix it. Even with a stick of 512 same as (other than size) the 256 that is in it it was still freezing without reason (that I can see.) I know that this motherboard can take 2 different kinds of memory. The book says:
"Memory Socket
* 168-pin SDR SDRAM module socket x1 and 184-pin DDR module socket x2
* Support 1 pcs PC133/PC100 SDRAM Module EXPANDABLE to 1.0GB, or 2 pcs DDR266/DDR200 DDR Modules Expandable to 2.0GB."
Anything else? Yes that's correct it will take 2 types of RAM...but it's one or the other...they can't be mixed.
Sometimes bad RAM will run good enough for the machine to boot properly but that's about it.
Testing it would be the best way to find out.
As far as the PSU maybe being the culprit the best way to test this is to borrow a known good one of the same wattage or greater and swap it in there and run the machine thru it's paces....

Best of Luck and let us know.