I have 2 WD hd's set up in RAID 0. I reformated my 3rd old drive and when I rebooted, I get the message, disk boot failure, insert system disk and hit enter. I have tried fixmbr, fixboot, bootcfg. No fix. I tried letting windows try to repair, no fix. I reinstalled xp on the 3rd non raid hd and windows shows the raid array. I just can't boot to the raid array.
I will ask the dumb question since you didnt mention it in your post. You did verify that boot order is correct in bios right? And even try to boot the computer without the 3rd hard drive installed? Because installing a 3rd hard drive should not keep the system from booting unless its trying to boot off that drive. If your boot volume was screwed up you might get an "nt loader not found" or something like that. Also make sure you dont have a USB device plugged in somewhere that the system might be trying to boot from.
This sounds like a simple fix vs. something complicated.
Originally after setting up the RAID 0 array, the 3rd hd had had xp on it as well causing me to have to choose which OS to boot to(slowing down). I used Partion manager to delete/reforat the 3rd HD. After the first reboot, that is when this happened. My RAID array was assingned E drive while the other 3rd non raid was assigned C drive. After the 3rd drive was reformatted, it changed my E RAID to C.
Then the pc would not boot. I think the OS still thinks its on E.
kg4 is correct. Your system actually had split boot/system drives. Your 3rd hard drive was the boot drive (containing the XP boot sector, boot.ini, ntdetect.com, and ntldr). The RAID 0 array was the system drive, containing the WINDOWS directory.
When you formatted the 3rd hard drive, you erased your boot drive.
You will need to do a repair installation of Windows to the RAID array, using F6 during Windows setup to load drivers for your RAID.
Alternatively, you could install Windows to your 3rd drive, boot it up, copy your data off the RAID, then do a full reinstallation of Windows to the RAID array (obviously, if you do this, do it with the 3rd hard drive disconnected to avoid setting up split boot/system drives again).