If you think it’s caused by malware and cannot start the machine, try the free Linux Avira Antivir Rescue system, here
http://www.free-av.com/en/tools/12/a...ue_system.html
Download it on a working machine, then insert a blank CD-R in the drive, double-click on the filename and follow the prompts to burn it. The file is about 50MB in size. On the infected machine, boot from it and when the loading has finished, click on the UK flag, then Start Scanner. Depending upon your computer, the scan will take about 30 minutes.