Have you tried running any programs like Spybot or Ad-Aware yet? When is the last time you defragmented your hard drive?
When does your system run slow? With those system specifications you shouldn't be running into problems.
Put your processor back at the manufacturer specified 3.0 gigahertz clock speed and see if that helps.
Overclocking can make a system run less stable. That is likely what was going on.
Perhaps... I have never overclocked AMD processors, but increased voltage usually does increase stability, at the price of increased heat.