Will not complete shutdown

[mayagrafix]

Laptop freezes during the last part of shutdown or suspend process.

An old laptop, which has a non working CD-ROM, was given a new life via Ubuntu (Precise Pangolin 12.04), by removing the HDD, then connecting the HDD inside a USB external disk enclosure to a 64bit desktop and installing from there. Upon completion, I extracted and re installed the HDD with the fresh Ubuntu OS back into the laptop. So far it works very well except for... shutdown and suspend.

On shutdown it goes through the motions until the Ubuntu logo screen with the flashing circles appears, then it freezes (with the CPU still running at 100%). For suspend it just freezes on the desktop. Even after waiting a long time when either of these situations occur the shutdown process will not complete, so I have to press the power button for six seconds in order to provoke a hard shutdown. However, when I re-start the machine it boots up normally and apart from the shutdown problem, everything else works OK.

The laptop is a Compaq Presario 2100 Notebook PC with a one core AMD Athlon XP-M @ 1.86Ghz, 512 megs RAM, and a ATI Mobility Radeon XPRESS 200M AGP 4x GPU.

Thanks for your help.