It's actually very common - and since SATA started being used - it's getting commoner (or should that be Proletariat?)
you say YOU fitted the disk - so you know how to get in
there are two cables connecting the disk and the PC and one has two ends.
so there are three points of failure (sata) or four if IDE
not that it matters in this case - but is it sata or pata (IDE)
sata cables (esp the early ones) seem to pop out at the drop of a hat.
IDE looks more reliable - but they do come loose
so open the box - disconnect and reconnect all of the cable connections (don't just push 'em in)
sata uses single connections - so it's reasonably straight forward
an IDE cable is (older version) 40 way ribbon
eIDE(newer) 80 way - in both cases the slave is connected to the middle - but do all 4
the power feeds are obvious
http://www.helpwithpcs.com/upgrading/install-h ard-drive.htm
http://en.wikipedia.org/wiki/Serial_ATA
oh and stop using system restore - it never does work
if that doesn't do it - it's going to be a BIOS adventure - more on that if we need it - later