Your problem I have experienced before and I have destroyed it. It CAN AND MAY depend on your specs of your computer, It would have helped us determine your problem. Here are some problems that may be conflicting wc3.
Too many programs at once running
Insufficient PSU (Power Supply Unit)
Defective RAM
IRQ Conflicts between certain hardware
BIOS setting problems (DRAM Voltage)
Corrupted dll files (game.dll could be corrupted)
Heat and Memory Leaks
Defective RAM/Motherboard/etc.
Virus
I fear for the second-last one because it will require sum major installation and reinstallion of Windows completely (well the Motherboard at least) email
whitefang_36@hotmail.com (my email) and I will try to fix your problem.
Note: People may wonder why PSU is involved! Its basically your power box that powers your PC completly, if its insufficient then it will cause crashes because certain parts are lacking power to run, thus cannot run at all. If you do email me or display your specs. Open your case, and tell me your Amps of your 3.3V, 5V, 12V lines (all +).