Odd Bootcamp behaviour: Chugging on OS change screen, black screen start-up

Question

Hi there. I have a 2-month old iMac with Bootcamp and Win XP installed. It ran OK for a while, but Bootcamp has started behaving erratically.
If I restart holding down the 'alt' key to bring up the Mac HDD or Bootcamp startup choice, when the screen comes up, it really chugs. The mouse moves once every second, and I cant actually choose the Bootcamp drive. I click on it, double click, etc, and nothing happens. I hit the power button to reset, and it eventually (after literally a few minutes) starts up in XP.
Once XP has started, it runs OK, perfectly fluid. But when I have finished, I try to re-start into OSX. I choose 'Shut down, and nothing happens. I choose 'shut down' a second time, and it turns off almost instantly, but when I restart the mac, I get the startup chime but nothing on screen at all – totally blank.
I tried restarting loads of times, but nothing worked. Eventually I unplugged it for a couple of minutes, started off my system disk, reselected the iMac HDD as the startup disk, and it restarted in OSX fine.
This whole episode really scared me, so I really want to stop it from happening again.
I have some ideas of what might have caused it, but need someone with a better brain than mine to troubleshoot my logic. Here are my thoughts.
1) Bootcamp in itself just facilitates the installation of windows and auto-installation of hardware drivers, etc. Once Windows is installed and working, Bootcamp has really finished it's job.
2) the 'holding Alt at startup' thing is an OSX thing (not Bootcamp specific). I reckon 1 & 2 together logically rule out Bootcamp the app as the problem.
3) The actual OSs and apps in either partition actually work fine once the rigmarole of changing from one to the other is done. So the problem isn't in apps or high-up in the OS.
4) Is it therefore a start-up/shutdown issue, present when either entering or exiting both partitions? As it's both partitions, could it be OS-independent as well?
This leaves hardware. Could corrupt P-Ram settings cause this (if it's still called P-Ram – I originally started using macs back in the days of MacOS 8.6). I'm guessing that the unplugging might have cleared the PMU, as sticking a reset button on the M/B inside an iMac would be pretty bad design.
Any thoughts?

Answer 1

Reset the PRAM and emptied the caches, etc.