|Try starting in safe mode. If you can, check those drivers to be sure you have the correct drivers for your components and version of windows. Use only the newest drivers for your products (from Dell's website) as reinstalling drivers from an old drivers disk may have drivers not compatible with the newer service packs your copy windows may now have.|
Also run Memtest to check for memory problems (even if it will not start in safe mode), just start to a bootable memtest disk and run. If you find a problem, retest with one memory stick in at a time, replace as needed.
In safe mode, you can do a system restore to a date before you had a problem, that also should help. If your computer came with a restore disk, you can return it to 'new configuration', but you would have to back up your files, as you will loose them, and you would have to reinstall programs (also accessible through one of the 'F' buttons on start up).
You have to be a little bit crazy to keep you from going insane.