hey tim,

Are you running vista or XP?
I presumed you have tried safe mode, last known good etc..?
If not then try the following
reboot the pc and tap the F8 key on the top row of the keyboard as soon as you see the DELL logo. Kepp on tapping the F8 key until you see a startup menu.
Select "Last Known Good" configuration and press enter.

If that doesnt work do the F8 thing again and select Safe Mode to see if that lets you in.

If your using Vista you might be able to boot to the VISTA disc and perform a startup repair or a system restore.

Let me know how you get on with the first two options though.

The first two didn't worked, but I finally got to a start up screen, thanks to your tip. Running anti-malware and will try system restore....

THANK YOU!