You are a bit short on info.
1. What OS? 2. Is start up disk a floppy or a CD? 3. Please elaborate on what you tried to do with fdisk and format and what actually happened. Hopefully nothing as these are dangerous unless you want to start aover and do a total reinstall of windows from scratch.
If your OS is Win98, try this. Boot from floppy and from the A: prompt type "sys C:" (without the quotes) and hit return. Then try to reboot as normal without the floppy in the drive. If that fails post the answers to the above questions.