Windows 7: Laptop suddenly freezing, radio and ping keeps responding.

Hi,

I have a T400 with Windows 7 64bit and 4 GB ram.
Once in a day or two the laptop suddenly stops responding, I can see the last screen / software I was working but when I press on the start or CTRL + ALT + DEL or CTRL + SHIFT + ESC no reaction is received. The mouse and Caps lock do respond, which means that the PC is not totally dead.
If I was connected remotely to a Unix session, I can still work and perform tasks inside the VNC but once again there's no response when I try to press on the start, or the CRTL + SHIFT + ESC.
I can ping the laptop and get a response but cannot connect to it via MSTSC or \\hostname as it is too slow.
If a radio was playing, it will continue to play and is not stopped.

I updated all Lenovo drivers, Run CHKDSK, defrag, MBytes.

Only hard reset solved the problem.

Please give me your advice.

Any one?