[Danyboy07]

I have an unwanted file MDM.exe in C:\WINDOWS.when deleted it reloads its self.there is also a file ravmon.exe in each hard drive.my anti virus detects it but can't remove it.tell me what to do.

[Curlyben]

Here's my usual C&P for cases like this:

When was the last time you did some serious maintenance on your system ?

System maintenance includes:
Defrag
FULL patching
Virus scanning
Spyware scanning
removal of rubish files

Defrag is an inbuilt function in XP.
Open My Computer > Right click C: > Tools Tab and its there.

To make sure everything is running fine run both anti virus and anti spyware apps in normal AND safe modes. (make sure that they are updated first ! ;)) (AVG is good and free AV)
(A couple of good removal tools are Spybot and Adaware)

ALso an on line virus and spyware scanner is Trend Housecall

Just a note: actively running two AV's on one machine can cause problems.
So if you are thinking about it make sure your current one is disabled first.
Same thing applies to online scanners as well.

Removal of junk files is easy with CCleaner a free app that does exactly what

If all this fails then a repair install may be in order:

Here's the official Micro$oft way of doing it,
and Here's one with screen shots.

Basically this installs windows over the top of your current setup.
So you don't loose any information you already have.

This lot should resolve your issue.

[ANETGames]

MDM.exe isn't harmful.
It is the Microsoft Machine Debug Manager.

I wouldn't advise removing it unless a virus scanner is alerting you that it is malicious.
Please be sure that whatever AV Software you are using is not rogue, otherwise it may attempt to get you to delete critical files.

However, ravmon.exe is a common name for many trojans and worms.
Here's what to do:
Disable System Restore (Optional)
Shut down your computer, then restart in safe mode (F8 On startup).
Log in, and then navigate to the ravmon.exe files, and delete them.
Now empty the recycle bin.
Then you'll need to use your anti-virus to scan your system. (Stay in safe mode if your AV will function in it).
After that, hopefully things shall run smoother.

Good Luck,