Yes, it sounds like the boot stripe is missing...
It would be great if you had an emergency repair disk to be able to fix this, but without one, you will have to manually go through the process or full rebuild.
If able to, I'd pop in another HD into the system without RAID, put an OS on it to be able to access this RAIS set and backup your data before you go any further to avoid a total lossof data. If you dont have a way to back up Gigs of data, then you can attempt to move forward without a backup, but at your own risk.
You should be able through your BIOS to select the RAID set as the First Boot Device or Boot device before any other Hard Drives, and as long as the stripe is not shot on the MBR ( Master Boot Record ) it should boot being that the RAID set is good.
If already set up this way, you can attempt a reinstall of your OS to the RAID set in which you select REPAIR instead of Clean Install, this will overwrite system data and replace the boot stripe etc. This is the easiest method, but you will have to perform clean up afterwards to reinstall games programs etc possibly that didnt like the repair process and clean registry.
You could also if you have another system of the same OS, use a bootable Floppy, Thumb, or CD or DVD to access the RAID controller and drop missing system files back onto the RAID set to try to get it to boot, but this is more involved and only is you see a message like NTLOADER Missing etc.
If you get a black screen without NTLOADER or any other missing files then, I'd try the REPAIR process through your OEM CD or DVD set that came with your system or OS upgrade etc. Boot off the media and select this method. Through the rebuild you may have to select F6 to give Windows the RAID drivers it will need to associate with the controller, otherwise it may try to install to 1 on the drives vs the RAID set. After pressing F6 after booting off of a Windows install CD or DVD and being prompted to do so in the bottom left corner of the screen you will need to put in the floppy, CD, DVD, or thumb drive containing the drivers. Easiest method is Floppy Drive, although MANY systems and users have done away with them years ago. This is one of those applications where a floppy is worth its weight in gold.
If you dont have any software for the RAID controller with low level drivers, you can try to perform the REPAIR install and see if Windows will detect the correct RAID drivers. 9 times out of 10 it will not have the latest drivers to associate, and the 1 out of the 10 time is usually because the controller is so old that the drivers have been bundled/integrated with the OEM Windows install like the older printer drivers etc.
Hopefully this helps!
Dave