Hello and Help Needed

I would try to run it again, it rebooted to get rid of the ones that it could.
You can take the memory test to see about the memory question, too.

Windows built in memory diagnostics isn't the best. I would suggest burning memtest86+ to a CD using imgburn and booting into that and let it run overnight. In the morning you can stop it where ever its at and if errors are found, I would replace the RAM. 3GB sounds like a good amount, but bad RAM could easily cause the problem you have.

In order to boot from the CD you will have to hit a key when you first cut the computer on (usually F8) and have it boot from CD.

Yes it is not the most accurate, but I think that it will suffice in this situation. Here are more basic instructions, if you care to use Petes suggestion
Guide to using Memtest86+ - Geeks to Go!

Run overnight or 6 passes.

Be sure to take a good stick and test each MB slot.

Looks like it might be. Read Petes and my post and take the test. I think you may need it.

All that matters is that it works, now. They probably had to be reset. One could have been loose, not fully seated. Use your machine and see if it works now. I think that it will.

It could be that one isn't in all the way. Reseat the RAM if you have not done so already. Has the computer sped up at all? Yocan also take a look at this: Optimize Windows 7

Which options to use, if any, are solely up to you.