MBR or disk problem?

My HDD is partitoned with FAT32 and has WIN 2000 and WIN 98 installed. I noticed occasionally i got the message “Cant find OS”. It happens all the time now.
I have tried to fdisk and FORMAT/MBR using an MS rescue disk and Partiton Magic boot disks,but get No Hard Disk message.
How can I get in to fix it up or is it a new HDD?
El Gordo