It would be useful if you told us which model computer and which version of Windows you have.  It sounds like a failed or failing hard drive.  First try the 90/90 hard drive diagnostics.  Restart your computer and immediately hit (all three keys at the same time).  If that doesn't run the diagnostics on your model computer, then boot to the Dell Resource CD and run the diagnostics from there.

Steve

Did this problem happen overnight or was going bad for a while ??

If it happened quickly it might be the Hard Drive.

if it happened over a period of time it sounds like malware and or spyware.

I did not say to press Cntrl - Alt  - Delete.  I said to press Cntrl - Alt - D  There is a big difference.

Steve

I have a Dimension 2100 with Windows ME.

Ok, I press control alt delete at start up and it brought up "Dell Dimension 2100 Setup"  In the menu it says: Main Advanced Sercurity Boot and Exit.  Where do I go from here? 

Oops sorry, I should have read more carefully.  Ok I tried control alt D.  I don't know if it worked, but somehow I managed to boot up windows in safe mode.  It is going very slow but at least I can access files and such.  I'm backing up files right now.  What do you suggest for the next step?  Thank you for your help in advance. 

Ok, I ran the diagnostics on startup.  It said IDE Diagnostics Primary IDE Fail Return Code: 7

Here is a list of some of the error messages I have been getting:

Stmgr has caused and error in MSVCRT.DLL

Winmgmt has caused an error in kernel32.dll

Scandisk has caused an error in SHELL.DLL

So does this mean I need to get a new hard drive?  Yes

Steve

IDE Diagnostics Primary IDE Fail Return Code: 7 means that your hard disk has failed.  If you are still under warranty, call Dell Tech Support for a replacement.

Steve