Can't start Win XP; black screen of death

Okay, this one is a doozy.

I have an old Dell computer that I pulled out of storage after 5 years. It worked beautifully, right up until yesterday when I decided to try connecting it to the internet. The machine worked fine at first, but then windows started downloading the last 5yrs worth of updates to XP. As soon as the machine forced a restart, it stopped working. Now, no matter how I try to load windows (normal, last known config, any kind of safe mode), I get no wallpaper, no desktop icons, no taskbar, no access to the task manager (CTRL+ALT+DEL doesn't work, CTRL+SHFT+ESC doesn't work), just a black screen and a mouse cursor.

Booting from the Windows XP cd is iffy. Sometimes it gets me to the screen where I can access the recovery console or try to run a repair installation of XP. (I ran the repair installation twice; the problem persists anyway.) Most of the time, though, as soon as the cd gets to the "starting windows" step (just before it lets you choose to install XP or go to the recovery console) it just crashes with a blue screen o' death and a Session3_Initialization_Failed error.

I think something is seriously wrong with some vital startup component (Ntldr, boot.ini, Ntdetect.com, Ntoskrnl.exe, or the registry), but the Win XP cd isn't fixing it, and I have no way of figuring out which it is. Somebody help!