I've been running Windows 7 on a WD 500gb SATA single drive, single partition setup for some time with no issues.
I've just installed a new Kingston V Series 64gb SSD and performed a clean install of Win7 to it, deleting the partitions on the 500gb and using that as a data drive.
All was well for a few reboots but then I started to get "DISK BOOT FAILURE, INSERT SYSTEM DISK AND PRESS ENTER" messages. If I put the Win7 install DVD back in the drive it boots fine.
Tried a clean install again, after replacing SATA cables and swapping SATA ports, with a complete partition wipe of both drives. Again, rebooted fine a few times then back with the "DISK BOOT FAILURE" error.
Looked on the web and found some discussions about it so I then started from scratch again.
This time I wiped the MBR on both drives using MBRWork, disconnected the 500gb and reinstalled to the SSD. Removed the install DVD and installed all the drivers which involved many reboots, all with no problem. To make sure I also did a few cold boots as well. Reconnected the 500gb, initialised, partitioned and formatted it. Copied data to it and did some more reboots and shutdowns. All was ok.
Then out of the blue comes another "DISK BOOT FAILURE" and again, if the Win7 install DVD is in the drive it boots fine.
So, is the SSD a bad'un?
It was a BIOS issue! I found a hidden away option for HDD boot order, which was separate from the usual HDD/CDRom/FDD boot order option. The WD was set to boot before the SSD... Swapped them round and all is well. Still don't understand how it worked at first though... Thanks Solaris