My TR2A won’t shut down - it hangs with the power light still on, the screen dark, and no disk activity.

I have to pull the power cord and the battery and let it sit for a few minutes before it will start up again.

I just repaved using the recovery dvd, so it is not a software problem.

I just installed a new hard drive and it behaves the same.

Any ideas which piece of hardware might be at fault?

Thanks!