I am have a HP Comqac Laptop,running Windows 8 and everytime I startup or bootup my laptop the start menu is present.
Will let me tell you something about windows 8 and windows 8.1
windows 8 sucks and so does windows 10
If you can why don't you downgrade to windows 7 pro that if you have windows 8 pro install on that computer.
Make sure your anti-virus software is up to date That could also be cause by a unknown virus or well hidden virus. So if you must you could try a virus software that you can boot outside of windows to scan your computer for virus it better then safe mode. or you could also get the fixmestick http://www.fixmestick.com
it is a external antivirus software that runs off the usb stick it boots right from the usb stick.
check your keyboard and see if the windows Key is stuck
or you can try this I know it will say windows 7 but it should work in windows 8 as will.http://answers.microsoft.com/en-us/wind ... 264&auth=1
your friendly neighborhood spiderman.