if you get a blank screen with no task bar and no desktop wallpaper at start, try unplugging all your peripherals and turn pc off and try again. see if it fixes it. If it boots normally, then it just becomes a matter of working out what is at fault, plug them each in one at a time, and restart pc to see what is to blame.
I had dying speakers and it took me 3 months to work out - I trusted them to not be the cause until they stopped altogether and it made it obvious. I had also upgraded my gpu around same time and was blaming it for the problem.
Another option is do a clean boot, this will tell you if its windows at fault or one of your start up programs:
https://support.microsoft.com/en-au/kb/929135
I know its frustrating when your pc suddenly stops acting normal and every start up becomes a game of Russian roulette to see if pc will start normally.