BSOD 5 minutes after computer start

Hello, I have very annoying problem with BSOD showing up circa 5 minutes after starting the computer: It happens only after the first start (sometimes also after the first restart) - I have been doing something for 5 minutes and suddenly - boom! - BSOD. Computer restarts and then it works perfectly... Only sometimes it crashes also after the restart. When I turn it off and turn it on again,...