System Running Slow after errors and windows repair (despite cpu usage being at 5%)

First, my specs:
Dell Inspiron E1705
Windows XP Home Edition (Build 2600.xpsp.050329-1536: Service Pack2)
Genuine Intel T2500 2GHz Dual-core
2 GB RAM
NVIDIA 7900 GS

I'm completely stumped on this. It is pretty much a long story at how I got to this point. Initially, when I did a typical restart (I had installed nothing new), I got a BSOD with this message:

"Bad Image Checksum. Image MSASN1.dll is possibly corrupt. Header checksums do not match."

Annoying, but eventually I managed to replace the corrupt .dll through the Windows Recovery prompt. I thought everything was ok, until I restarted and got ANOTHER BSOD with the message:

"Stop: c00021a (fatal system error) session manager initialization system process terminated unexpectedly with a status of 0xc000026c. (0x00000000 0x00000000)"

This was much tougher to figure out, and I ended up not being able to find much that applied to my situation. So, I did a Windows Repair install. I thought this would be the end of my problems, but no. As soon as Windows booted up, it took about a minute to log in. It displayed my desktop and icons ok, but not my start menu. I could right click once, but nothing after that. I can't open anything or highlight icoans and the start menu never comes up. It took forever for me to finally get it to boot into safe mode, but that has problems of its own. My cpu usage is about 5-6%, but everything is agonizingly, nearly unuseable slow. Just dragging the taskmanager window causes CPU usage to shoot up from 2-3% to 50-55% (or any window for that matter). It took 10-15 minutes for system restore to come up, and reverting didn’t work. It just froze my laptop. I tried running Norton's, it just doesn't respond when I try to scan. Spyware Search and Destroy just freezes half-way through. Trying to even get malwarebytes on my laptop under such conditions is very difficult. I’ve given up on that fact. I haven't messed around with the internet, since I've got this old desktop to use.

I've ran checkdisk from the recovery prompt, and that didn't do anything. Neither did the checkdisk before Windows started up. I did manage to get ComboFix to work (it detected and removed Memman.vxd and skinboxer43.dll) as well as hijackthis, though I'm having trouble getting that log to this computer. It seems it doesn't register flash drives at the moment.

Before this, my computer was alright (I had some frame-rate stuttering during games, but I am pretty sure that is unrelated, due to a fan that I was planning to replace). I’m getting really frustrated with this and I’m just looking for new options/answers before I try fully re-installing windows or doing a format.

Brief Edit: Just noticed this, the hard-drive working light on the laptop is constantly green. May or may not make a difference, just thought I'd mention it.