iMac starts itself with reboot screen

[hbennett]

In the last three days my iMac desktop has begun starting itself up. There is an audible beeping (three or four beeps) and the on/off indicator light blinks rapidly. When the screen comes up there is no desktop but a gray background with reboot instructions. When I type the reboot words "mac-reboot" the desktop comes back.

Under Logs in the system profiler I see the following message:

CGXDDisableUpdate:Updates disabled by connection 0x66-3 for over 1.000000 seconds

and

CGXBlindSurface returns-536870210

The computer is rather old, is running OS X 10.2.8 and has never done anything like this before. I would like to understand what's going on and whether this indicates that I should be doing something?

Thanks.