Fair enough. It's just that we get a lot of end users popping in looking for help troubleshooting their own computers, and we get a bit snippy about that.
But it sounds like you're just a green technician, and that's a different story. You're certainly welcome here.
I recommend you get up to speed on basic hardware troubleshooting as soon as possible. If a customer came to you with these same problems, you want to be able to handle it. You really don't want to hand it back saying, "I don't know enough to fix this." You'll lose customer quickly. Of course, it's even worse to pretend you know how to fix it and screw things up!
At the very least, you'll want to have a couple of known-working video cards, a PSU or two, and some commonly used sticks of RAM. That way you can swap out parts and help isolate the problem. You also need a few good live CDs. If the computer can boot up with a live CD, that goes a long way toward eliminating possible problems.
Anyway, search the forums for this stuff. I'm a bit pressed at the moment, but I may be able to dig up a few recommended threads for you on the subject a little later. Good luck with your business!