Very odd Xbox behaviour.

I turned on my Xbox this morning and was listening to some music from the on board hard drive when it suddenly stopped and crashed.
When I tried turning it back on I got 3 red lights.
I unplugged my iPod, external HDD and the network from it and tried to power it on again to no avail.


I then removed the HDD from the top and tried powering it back on and it powered up fine and works.
I checked the contacts on the hard disk and put it back on the top, powered it up again and it works fine!

Any ideas? Am I a few power ons from complete console death?

I'm unable to find my receipt to get it repaired.
Any idea on the best thing to do if it does blow up? Can Microsoft glean much info about when it was manufactured from the serial number?

I don't want to be without my Xbox!