Just curious ...
Did you try pressing the F8 key at startup to launch the boot menu?
Once that comes up, select "Last Known Good Configuration"
Windows will then attempt to reboot using the configuration from the last complete startup.
You should open your case and make sure your cpu fan is spinning. This is also a common error that is related to an overheated cpu.
Since you are still running SP1, (depending on your media cd) you can also boot off your Windows cdrom and run a Repair Install. It won't affect any installed programs or data and will generally replace any corrupted files.
Or, if you just want to make sure you have a nice clean installation, Moishe's suggestion is great. After all the software I test, I tend to want a nice clean installation after about a year. Once you have your clean install all patched & updated, run a Microsoft backup & save it to an external disk so you won't have to repeat this process again.