|You cannot really repair it using a reinstallation disk unless you just want to reinstall Windows from scratch.|
First thing to try is to start the computer in 'safe mode with networking' (keep tapping the F8 key at boot to get into the safe mode menu). If the computer starts without the warning then download, install & run Malwarebytes to remove the nasty and then remove the start-up link to it by using the tools/startup section of CCleaner.
If the warning still appears in safe mode then it's a bit more difficult to remove but try the easier option first and post back if you need further help.
"I've always been mad, I know I've been mad, like the most of us..." Pink Floyd