Sounds like your hard drive has either failed or one of the leads to it has fallen loose. Check the wiring to make sure everything is connected correctly. Also check the BIOS to make sure the hard drive is listed as the first disk in the boot priority column.
You're gonna need tech support. If it's a RAID system don't forget that the Raid controller needs to be on. If it's a SATA drive, make sure that SATA port 0 or SATA drive 0 is turnd ON in the Bios, and the others that have no drive plugged into them are turned off. Make sure you disconnect all external flash drives and hard drives. Take any disks out of the cd drives. If it's still unbootable and you have windows vista you can try windows startup repair from the windows recovery environment.