I have a VPR Matrix model 2020.
Pentium 4
2.0 Ghz
1256 MB DRAM
Windows XP SP2
Geforce 6200 w/ 256MB 8x AGP

I recently had a power outage that fried my power supply. I had a 550W power supply in the computer. I replaced it with an old 300W that I had laying around. Since then everything about my computer seems to be going in slow motion. The properties in "My Computer" still show 2.0 Ghz Pentium 4 with 1.25 GB of RAM. I'm wondering if the smaller power supply would cause the slowness, or if the power outage may have possibly damaged some internal components such as the CPU or RAM chips?

how many ram modules do you have? Because the power thingy may have damaged one of your modules and not the others

I have 3 RAM modules. 2 of them have 512MB chips in them and the third has a 256MB chip. I used the windows defrag tool to analyze the hard drive and it showed 20% fragmentation and 62% usage. So I've set it to defrag, which has been running for nearly 12 hours now and is nowhere near finished.

try defragging in safe mode you'll have less programmes so less restarts