I had a problem with my PS3 40Gb overheating and going into turbo recently. Found it was pretty clogged up and that having it on its side rather than laying it flat helped significantly.
I also had a problem where I killed the power using the hard switch before I had turned the console off to standby (I know, don't ask) which caused it to freeze just like you describe. I found it was the HDD and it required a format of the drive (which lost me my saves, so back them up if you can) but fixed it straight away. The only thing I can think of is something got corrupted on the working space of the drive. Worth a shot if it's not just overheating.