I just got the same problem.
Do not panic.
1) Unplug the system, and leave it unplugged. Then, plug it back in.
2) Take out the hard drive, wipe it, and put it back in.
If it still doesn't work:
3) Call Sony and ask about their repairs program.
If they charge you the bullshit $150 price:
4) Get it fixed by a third party.