You can try a rebuild planner.
Go to Services, enter on your remote, 4 0 1 and then, ignoring what's on screen, press Select. Choose option 7. This will rebuild the planner and should clear out any hard drive errors (it takes about ten minutes to complete) and it won't delete your existing, recorded programmes.
You can try a reformat.
Switch off at the mains
Holding Left and Right navigation buttons, switch power on and hold for about 30 seconds until Green play light comes on
Press 'Select'
The 'play-light' will then rotate clockwise while the resetting procedure takes place. This may take up to 3 minutes. (this timing could vary if there are no programmes stored in the hard drive)
It then reverts to 'Standby'
Leave the machine for 2 minutes while hard drive reformats.
Just some info I archived for my own benefit. Use at your own risk.
http://www.skyuser.co.uk/index.php?categoryid=1
Is a good place for resolving Sky issues.
Let us know how you fare.
Good Luck.