Check graphics cards drivers are up to date. A program could be a bit too much for it now and again.
Also concur with BOAC's untick 'Automatically restart' in System properties. That'll be the easiest thing to start with.
Give
Msconfig a look at for your programmes that run at startup. That may improve start times.
PS. A 'relatively uncluttered Desktop should have no more than 10 icons on it!
PPS. How much free hard drive space do you have on the drive that Windows is installed on?