Here you have some of the relevant information about the last three crashes:
Probably caused by : nv4_disp.dll
Probably caused by : ipnat.sys
Probably caused by : hardware ( c6501+c4e46 ) (c6501.sys is the CMedia sound device driver)
A more detailed analysis confirms that errors are spread between unrelated drivers and modules.
This isn't normal with bad drivers. It's more often related to bad hardware, especially RAM since software in memory can be corrupted because of bad read/writes, so the CPU at a certain point can execute an illegal instruction that shouldn't have been there and the computer crashes. There's an interesting fact, though: one of the dumps hints about a sound device error.
I can't do anything else but, once again, suggest to update sound drivers and test the RAM with Memtest86 and Prime95. Easy to do, but not the only thing to try.
You have, in this thread, a lot of different hints: fans, hard disk, ram, psu. You can check all those by yourself.
To test the HD use HDTune, more info on the official site (and even in this forum).
To test the file system issue a chkdsk c: /f from a command prompt.
You could additionally check the system files for errors via System File Checker.
There isn't much else I can do now. Each program mentioned is this thread is straightforward to use and almost self-explanatory, but the official sites have short, understandable manuals in most cases.