Yeah, there is either an MBR problem or your actve partition - either C or the 100MB system partition has been deactivated
Download this program
(last entry on the webpage) and burn it to CD. Then load from this CD and look for the following:
1. Do you have a small 100MB partition and is it marked "Active". If it is present and not active, set it to active. The controls are in the Partition tab > Modify. But you have to highlight that partition first.
2. If there is no 100MB partition, is the C: partition active. If not, set that one active - same way (highlight > partition tab > Modify)
3. Click on the Partition tab > Build MBR
4. Click "Apply" > top left
Then try to boot your system.