Having a serious problem with my system

hello everyone,i have a really deep and serious problem with a virus on my system,whenever i reboot my system a pop up message appears just before the start up ,written"hello damagum(damagum being my pc's name)don't worry i am a nice friend"and i have to click on ok before it goes off.i don't really want reinstalled my os because i have some important files in my c drive.is there anything i can do for this kind of virus?

I'm kind of thinking that it's not a virus, but rather that someone put a logon message on your computer.

To see if that's the case, try the following (registry editing can cause damage if you do the wrong thing. If you're not comfortable with it, have someone do it for you).

Click on Start > Run

Type in regedit and click ok. The registry editor will pop up.

In the left panel you'll see headings. Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\

Click on Winlogon once with the left mouse button.

In the right panel you'll see a key called "LegalNoticeText". See if that message is in there. If it is, double click on "LegalNoticeText" and delete the text you don't want.

Click Ok.

Exit out of the registry editor, reboot your computer and see what happens.

tnx adweston,i' ve tried and it really worked