If it's starting, getting to this screen, crashing and going through the cycle again, chances are good it's a registry error. First try booting in safe mode when starting up, if it does the same, throw your O/S disc in and select boot from disc. This should then allow you to repair the current installation, though you may lose a bit of data in the sector that's gone faulty.
There are only 2 tools in life: Gaffa tape and WD40. If it moves and shouldn't, use the gaffa tape, if it doesn't move and should, use the WD40.