|Ok lets see if you can get into the admin account or if it has been compromised. Get to the safe mode screen (I'm assuming u do use Vista) by tapping F8 on startup, bring up the black screen menu, select boot to command prompt. Hopefully it brings up the command prompt box. Where the cursor is in the box type this noting spaces|
net user administrator /active:yes
if the command completes successfully the administrator account will now be visible for access, note there is a space after the word administrator. Reboot and tap F8 and this time try logging into "safe mode with networking", it should load and bring up your normal user account and the admin account, click on the admin account to login. If you are able to login here, then follow XpUser4real's suggestions above and see how that works out. Personally, I use a program called "combofix" to remove this follow by malwarebytes scan. If you get the same window popup you are in for a fun time.