Computer freezes and exhaust fan speeds up?

Apple – Support – Discussions – EMERGENCY!!! …. Looks like CMCSK has solved it.

Disconnect all peripherals from your computer.

http://support.apple.com/kb/HT2183

System Preferences/Network/Location:Automatic/Highlight Airport/Network Name:your name/Click the Advanced button/Airport/Preferred Networks:Select your name/place a checkmark next to “Remember networks this computer has joined”/lock the padlock.

Boot from your install disc & run Repair Disk from the utility menu. To use the Install Mac OS X disc, insert the disc, and restart your computer while holding down the C key as it starts up.
Select your language.
Once on the desktop, select Utility in the menu bar.
Select Disk Utility.

Select the disk or volume in the list of disks and volumes, and then click First Aid.
Click Repair Disk.
Restart your computer when done.

Repair permissions after you reach the desktop-http://docs.info.apple.com/article.html?artnum=25751and restart your computer.