Your cpu temp is too high, it's probably what's causing your freezings and crashes. Turn the computer off, unplug the power cord, open the computer case and use a can of compressed air to clean the dust out of the CPU fan and heatsink, also clean the video card fan and the PSU fans (I think there are 2 on this model, one at the rear and one at the bottom). Then replug the computer, turn it on and check that all the fans are spinning properly.
If there's no dust at all check that the CPU fan and heatsink are seated properly and don't budge at all. Recheck the CPU temp in the BIOS.
What program did you use to monitor the CPU temp within Windows ? Software readings may be erroneous if the program uses the wrong sensors, the values in the BIOS are the most accurate ones. See if there's some Asus PC probe program on the motherboard CD or download it from
here under utilities.
By flagged devices in the device manager I meant devices with a red cross or a yellow exclamation mark in front of their name (like on
this pic for instance), there shouldn't be any.
The errors in the event viewer are probably caused by the crash, not what's causing it. The ASInsHelp service error happens because AI booster or Asus cool&quiet aren't installed. You don't need those programs but installing then uninstalling them should solve the issue.
The Thermaltake XP550 NP power supply is not a very good PSU, more like a low-end 300W model according to
this review from X-bit labs. The +5V line is nearly out of specs. Your computer shouldn't be a power hog but see what
extreme outervision's PSU calculator says about your max power requirements : enter your complete specs, set capacitor aging to 30% and add another 30% to the final result to take the PSU's average efficiency into account. See if you can get your hands on another good quality 400W+ power supply, look at the recommended models for standard computers in
this thread.