Cannot start Windows Vista

When I try to bootup my pc I get a black screen with DISK BOOT FAILURE, INSERT SYSTEM DISK AND PRESS ENTER. I also have a Blue Screen DRIVER_IRQL_NOT_LESS_OR_EQUAL.

I bought your recovery disc& got as far as System Restorebut my OS was not found, but I managed to do a System Disc Test.
Result completed successfully
Error Code = 0x0
Time taken 0ms

Root cause found: A hard disc could not be found. If a hard disc is installed, it is not responding.

Are these System Test's result's to be trusted, because I take it to mean that I need a new HD. I would rather not take the pc to a repair store, as they would charge me for looking at the machine, and the money saved can got towards a new HD. I hope this makes sense because it is 03:11 & I am tired. Thanks Mac
I've known several occasions where a "missing disk" was really a poor connection.
Disconnect/reconnect all of your HDD power and data cables several times to clean the contacts. (for a laptop eject/reinsert) and try again.
Enter the BIOS setup and see whether it reports the HDD as being present.
If it's still missing, check by touching the case as you power up (desktop) to feel if you can sense the vibration of it spinning up.
If it seems dead, check that a different power cable doesn't revive it (swap with another device if possible).
If you have access to an external caddy, see if that gets it spinning.
Only when you're convinced it's "left this mortal coil and joined the choir eternal" get yourself another HDD.
If it is still alive, you can usually get a free diagnostic utility from the website of the HDD OEM which will tell you if it's toast.
Report back if there's any sign of life.