Is Windows XP too old for my computer?

I think it's possible the guy (or myself) could be mistaken, but he doesn't intentionally mean to mislead me, I've known him for quite some time, he's not the lying type.

As for taking it to him each time there's an issue, I haven't done that the past two times, I went to someone else(Circumstances beyond my control), and they didn't do nearly as good a job as he did, he's at least three times the technicians they are.

As for the parts, I picked those out myself, I know they're compatible with each other, but hopefully they aren't shoddy >////>

Regardless of whether he's deliberately lying to you or not, what cannot be denied is that he's one of those type who fancies they know a whole lot more than they actually do. Like the person who thinks they're some kind of master auto-mechanic because they could follow the instructions in a repair manual for changing the oil. These people are probably more dangerous than the average idiot who really doesn't know anything, but at least admits they don't know anything.

But with so little detail to work off of regarding what the one guy usually does that the others didn't, it's difficult to say for sure. We'd need more details on what the various places actually did. Someone like the guy you describe might think that registry cleaning programs are some great and glorious tool, never once stopping to ponder why Microsoft hasn't bothered to include such functionality into the OS for all these years. Not doing a little research to find out that Microsoft actually made the first registry cleaner, then quickly pulled it because they found it was causing problems. Not taking the time to put those two pieces together and draw the rather obvious conclusion.

Since this is a custom machine, that means most diagnostic tools won't really work and it's down to the drawn out and tedious method of testing everything one at a time.

So since you say you recently reinstalled the OS, that's where I'd start. Reinstall it again, making sure to format the drive along the way. Install only the bare minimum of programs. Get it up to SP3 and then all the updates after that, but install only the drivers and then the absolute bare minimum number of programs you need to be able to get by for about the next week. If the problems persist, you've narrowed it down to either hardware or some kind of issue with those specific programs you've installed. So assuming for example you usually use the full Adobe Creative Suite, but this week you could get away with only installing Photoshop, only install Photoshop. If you can go for long periods of time without issue, where you normally would have had issues, add one additional program and start the testing over again. Rinse and repeat until either everything is installed or you start having problems. If you're still getting issues, you're PROBABLY looking at a defective bit of hardware. So get yourself a copy of memtext86+ and let that run overnight. Even a single error is too much for RAM, so if you get any errors at all during your testing you'll need to test each memory module individually by physically removing the rest. If you find a defective one, send it in for a warranty replacement.

If the RAM checks out fine and you're still getting issues, you should remove any hardware from the system you don't absolutely need. Run like that for a week, see how things go. If they work well, add ONE piece of hardware back about every week and test in between. Same as with the software, rinse and repeat until you've either got every bit of hardware back into the unit and it works great or you isolate the problem component.

It's boring, it's tedious, but it's also the only way you're going to not just be fumbling around in the dark hoping you stumble across the solution by dumb luck. It's also ultimately less painful than dealing with the current crop of issues ad infinitum.

I do pretty much plan to do just that, when I'm able.