Random Keyboard and Mouse Freeze

Hi there,

My rig is a Dell Inspiron 530, iDeneb 10.5.5 .
been running great for about 18months now, but in the past few weeks im getting an incresingly frequent problem where the keyboard an mouse will just stop responding entirely.

so far i has always been while firefox is running, (may also have happened with other browsers but im not sure) usually when i get up and leave the machine alone for a minute, when i come back it won't respond.
it never happens when im actually using it, only when i turn my back on it for a few minutes.

plugging out/in the keyboard and mouse does nothing. only a hard reboot solves the problem.

also, may be related, sometimes when i reboot the machine, when i get back into the operating system the keyboard will not be working.

none of this has ever happened on the Vista partition on the same machine.

(Keyboard is Microsoft Comfort Curve 200, and a Logitech wireless mouse)

any help or insight would be appreciated.