The CPU sounds like it is always running a big program or something, with the humming noise, when it is doing nothing.

Windows version, computer specs?

Windows XP

Core processor 3800+
2.00 GHz 896 MB of RAM

Need other specs? If so, what else do you need?

How is CPU usage in Task Manager?

it varies from 0-40% with normal activity

You may want to post HijackThis log at Spyware, Adware, Viruses and HijackThis Logs

Okay, i'll do that.

also, images don't load up most of the time, or they load up with white bars across the middle of them
the computer lags when I scroll
and it won't let me paste screenshots. it says "Error getting the clipboard data" and then "There is not enough mempry or resources to complete operation. Close some programs and then try again" and paint is the only program open.

Make sure, your computer is clean, first. Go to my link.

it says something about the clipboard

You need to post what it says, EXACTLY, not something.