Why EXPLORER.EXE and MMC.EXE Keep crashing on Window 7 ?

Sir, I was using window XP for much longer time and then i installed window 7 in my computer I have successfully installed it from 2-3 weeks it works properly but after some time it repeatedly gives explorer.exe crashes. I am finding solution for it and then one problem is also stand for me which is that the MMC.EXE is also start crashing. I have tried many solution to solve my problem but still not get relief from this problem. So, who is expert here can just tell how can fix this problem ?