Computer stuck in boot loops with corrupt secondary operating systems

While this ability to install use multiple operating systems on Macs is convenient, in some instances problems with a non-Mac OS X system installation can prevent users from being able to boot back into Mac OS X.

Apple Discussions poster clv92 writes:

"I have parellels on my iMac but I sometimes still restart in windows using boot camp. When I tried to restart using boot camp today I am stuck in a loop of windows xp starting and trying to run diskcheck, not finding it and trying to restart windows again. It just goes in a loop."

Holding various key combinations to boot into a healthy OS X partition may not work for users, resulting in no apparent way to get the computer to boot again. This kind of problem usually indicates the computer's PRAM, which holds boot volume information, is set to boot from the problematic drive partition. Additionally, the PRAM settings might be corrupt, which may prevent some of the bootup key commands from working properly. For users stuck with this kind of problem, the key is to reset the PRAM and then immediately manually choose the desired boot system.

Fix: Reset the PRAM and choose the boot system When the system resets again, hold down the options-command-P-R keys all at once and let the system go through a few reset cycles before releasing the keys to let the computer boot normally. Immediately after releasing the keys, users should hold the options key so the system goes right to the boot menu instead of attempting to boot from the default OS (which could be the corrupted OS that could have caused the problem in the first place). When the boot menu loads, select the healthy operating system disk and press enter. This should allow the system to boot properly.

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