error message : logon UI.exe over run stacked buffer.

This in my opinion is a malicious virial attack. I have tried every back door exit known to me to get windows to load but to no avail. It's like it's running a long winded script in the background. I can't get to anything to get rid of it ex. windows defender, system restore,even the bios and HP diagnostics don't work. Any ideas? Thanks Mike.