IMAC locks up

New to the forum so howdy.
Seems like after going to mountain Lion my Imac locks up after sitting over night .
It Looks up but it is unresponsive with the spinning wheel . It Is a slightly older
Imac 2GHz core 2 duo 6 GB mof memory . I've had the G drive I use for the time machine
having issues also and have to take it off line and back on for the mac to see it.
Related ?

Run a verify and repair check on your internal hard drive by booting to the Recovery partition (command + R) and using Disk Utility. Since the machine is an older one the drive may be experiencing errors. Also, how full is the drive?

Thanks I'll check that out tomorrow. The drive is at about 200 of 250.
I think I might un plug the G drive(time machine) also tonight
I did see this in the logs also Just before we tried to get on.

WindowServer[100]: handle_will_sleep_auth_and_shield_windows: no lock state data

Thanks again I'll let you know what if anything I find.
bob