Why does my PC start out processing fast then come to a crawl after about an hour?

Memory leaks.

When you run a program it uses a certain amount of memory. When you terminate the program, it should relinquish the memory it was using.

In Windows, this doesn't always happen. So, after a while there is less memory to go around, and so programs have less memory to use, and they need to share it. So, they take longer.

The best possible fix is to format your hard drive and install Linux.

Alternatively, you can set the defragger to run once a week.

You can look at your process list and see which programs suck the most memory, and try terminating them. BEWARE: explorer.exe is a memory hog, and you will want to kill it. DO NOT! If you do, you will have no desktop, no folder access, and basically, no computer.

All web browsers use a lot of memory, some more than others. Internet Explorer and Google Chrome use more than Mozilla Firefox.

- sounds like you have lots spyware and probably tons trojans infested your System32 and making use of your system resources.

cheap solution would be to download AVG Free Edition and something like Spyware Search & Destroy (free also) and try to get rid of whatever they picked up.

if you want something more I would suggest Nod32 $25/yr works like a charm. they also offers free 30 day full function demo which is also (free)

if you are more pc literate :), and there are nasty bugs that just wont go away go for a copy of Hijackthis (.exe) be very assure of what you are doing because it force-delete on things you tell it to : |

upgrades:

could use some ram upgrade as well. make sure you know what kind of ram your pc is using at the time. match the same type or even brand if possible.

My guess is you have spyware that your antivirus doesn't pick up. Download malwarebytes free version and run it to clean up any left over infections.

Also press ctrl & alt & del and go to your process tab to see what is using all the memory or cpu cycles