try to write new MBR... from the following steps.
1. first boot your computer through floppy or CD
2. then type fdisk /MBR.... this write new MBR in your hard disk...
3. if this will not work try to use Anti virus software...
If other knows best step other thant this please send message to my mail - id ( yadeeny2001@yahoo.com)
J.Sudhakar
October 2005