runtime error

Hello everybody!

Hope I can get some help...when I power up my system I get this message

runtime error
C:\winn\system32\svchost.exe

and if I click on anything after this point it locks up on me and I have to shut the system down by holding the on/off button for 5 seconds to shut it down

this only happens about 1 out of 5 power ups...it does not happen all the time???

It is a pain in the tail to have to redo everytime this happens...
thanks for any possible help