iMac won't reboot
After deleting some files to clear up memory yesterday (no operating systems, just photos), my rather elderly (about five years old) iMac froze so I force rebooted. The white screen comes up (with the usual start 'chime') then about five minutes later the apple logo appears. Five minutes later, it spontaneously restarts, and so the loop continues. I have tried starting with the shift key held down, but nothing changes. Any advice on what to do?
iMac, Mac OS X (10.5.1)