If you are clean of viruses and malware, then it sounds like the computer is overheating. CPU intensive activity, such as playing games and converting videos, will increase the temperature. Windows will shutdown as a precaution.
When was the last time you opened the case up and cleaned it out, paying special attention to the heat sink/fan? I thought I was keeping my heat sink clean, using the usual method of canned air and blowing it out. Not so. One day I took the whole thing to the kitchen table and it was then I could see that down inside the grills it was still full of crud. (We have pets.) I removed the fan and used tweezers to pull the gunk out. Then I gently cleaned it up with alcohol and q-tips
If that doesn't help, then the fan on the heat sink could be dying. Been there, done that too. Heat sinks aren't that expensive to replace. If it needs replacing, it's best just to buy a new heat sink too. Upgrade to the fastest fan speed/capacity suitable for your system, especially if you've been running on the factory installed one all this time. Manufacturers usually put in the minimum-cheapest ones.
Since you mentioned noises, it could just be the heat sink/fan. But if all that didn't help, then it could be the power supply. I don't know anything about those, though. And lastly, the noises could be signs that your hard drive is failing. Been there. Done that.
Now, about cleaning up and recovering some of that space on your hard drive. There are lots of things you can do to recover space on it.
1. Uninstall any old programs you don't need or want anymore.
1a. How many pictures are stored in My Docs that you don't look at anymore? Move them to copies on CDs for safe keeping and delete them. Same with music files, if you're not really using them. Backup any data you're keeping in My Docs and get it out of there if you don't need it often.
2. If System Restore is set to the maximum, dial it back. Mine is set on 2%, which for me goes back 5 days. You may want a little more, depending on how many automatic restore points run for you. But honestly, who needs to go back two weeks or more? It might work to fix a specific problem, but you end up with a bunch of renamed files and folders, and/or reinstalling recent new software.
3. You can start recovering space just by using the basic Windows Disk Cleanup. There are also software programs that will do more.
Once you've cleaned the excess off your hdd, then run scandisk on boot. After that, run defrag.
You should see a marked improvement on performance, as long as we've eliminated any serious hardware problems.
P.S. When converting videos, it's a good idea to do that when you aren't doing anything else on the computer. No browsing, emails, playing games, etc. Not only does that keep your computer cooler, it also lessons the chance of errors during the conversion.
Edited by mommabear, 31 March 2008 - 02:29 PM.