Have you tried switching off when it has booted up then switching it back on again.
I have the same sort of problem usually a restart works ok.
I was thinking maybe a faulty switch on button making a bad connection.
Did a factory restore about a month ago and everything was going well but the old problem has started again.
I was also thinking maybe a faulty PSU as it sometimes grinds to a start.
I gave up trying to fix mine but will see if you get any good information that solves your problem as it may help me as well.
I tried most of the usual things defrag.chkdsk.Updated drivers.ran Security programs.scannow.
Never made the slightest bit of difference.W/7 64bit.Medion just in case yours is the same.A very quiet PSU on it so you can hear the slow start up and sort of starting and stopping as it gets to the windows screen.
So not sure if it could actually be the hard drive but the computer is only six months old.
I could send it back for repair but it has to go to Germany so just putting up with it at the moment.it has been like that since I got it.
Anyhow best of luck with yours I hope you get it fixed.