on your computer - just the operating system, it might be worthwhile starting from scratch.
If you have a Windows 95/98 boot disk (floppy) boot your computer from this, and use the fdisk facility.
Once in fdisk, do ask follows:
1) Remove any logical partitions you have
2) Remove any extended partitions you have
3) Remove the primary partition.
Now restart fdisk, and go in opposite direction:
1) Create a primary partition*
2) Create an extended partition (if required)
3) Create logical partition (if required)
*If you have other partitions don't forget to make the primary partition active.
Having finished with fdisk - reboot.
On restart, still using the boot disk (floppy) format your C drive. Once formatted it should be ready for your operating system.
hope this helps