Tech Help Please: PC Too Slow

I don't know if this is a Hardware or Software problem, but I need help.

My PC: Pentium 4 2.8Ghtz (HyperThreaded), 1GB Memory* (2x512MB DDR400), Motherboard:MSI PT880 Neo-LSR (MS-7008), 120GB WD HD (FAT32), WinXP MCE 2005, ATI Radeon 7000/VE 32MB AGP** (old, I know)

Background: I thought I'd be nice & salvage my Mom's pics from another HD out of a dead PC. Hooked it up wrong, 2 masters, forgot a jumper. Set it right & PC went into a re-boot cycle just after the Mode Selection page (Start in Safe Mode, etc) Did overlay reinstall of XP, PC slow, salvaged pics. Did 2nd overlay reinstall when on-board sound driver didn't take cause I tried the wrong one.

I tried replacing the power supply since I had similar syptoms & that fixed it before. I checked each stick of mem - no change, *added 2x512MB for 2GB total, no change. **I changed out my Video Card from Nvidia FX5200-VT128 since I had problems with it before, no change in speed.
I've updated all drivers, ran HJT, AVG7.5, Ad-Aware2007, everything short of a reformatted new install. I don't have much on here because I can't do much to begin with. I can only run one program at a time.
AOL & Media Player 11 practically lock the system up when ran together. This thing is slower than my old 366Mhtz laptop.
Any advice? Questions welcome.
Thanks in Advance.

 

Have you checked to see if the devices on your IDE channels are set to DMA mode?

 

So, you "Set it right". What, exactly, does that mean? What were the final master/jumper settings?

And, you "Did overlay reinstall of XP". Why? All you needed to do was install the hard drive from your mother's computer as slave. So, why did you do this "overlay reinstall of XP"?

 

Novice - I'll have to double-check that, but my BIOS is set to auto-detect my drive(s). Never had trouble before.

usafveteran - I messed up in that I didn't set Mom's 40GB as a slave. "Set it right": My 120GB was set to master and Mom's 40GB was set to slave. It was the master in the dead PC, had WinXP Home installed on it.
I did the overlay because my PC went into a re-boot cycle just after the Mode Selection page (Start in Safe Mode, etc), I couldn't get any futher into Windows, not even in Safe Mode, it was completely stuck in that cycle. And I've got about 50GB of stuff that needs backed up before I reformat.