One Care requires an active internet connection to install and like most antimalware software would not install properly on an infected computer. Try booting in to Safe Mode with networking. To boot in to Safe Mode restart your computer and after the bios beep press the F8 key repeatedly. When the boot options menu appears select Safe Mode with networking. After entering Safe Mode go to this site and run the online scanner -
http://www.eset.com/onlinescan/ When the scan completes restart your computer, go to the One Care website and follow the instructions to add another computer -
http://onecare.live.com/standard/en-us/install/addcomputerinstall.htm
Jim - MVP Windows Live - Forum Moderator - Live One Care - Live Mesh - Microsoft Security Essentials