Envy 750-114 will not load windows

[Dirk7]

My Envy 750-114 desktop will not load windows. This is a recurring issue, starting back about 3 months ago. When I press the power button to turn on the computer, it the bios screen comeshot on for about 0.5 seconds (seems normal), it proceeds to the Windows pre-load screen with the little progress circle balls (also seems normal), then the screen goes completely black briefly (as if it is receiving no video signal from the computer, but again normal), and then it goes to a different black as though it is receiving signal from the computer, this is where the startup appears to stall.  We have been to the Geek Squad several times and they are helpful but seem to be baffled by the problem as well. I should add that the system seems to work usually when we present our case  to the teclinicians.  But they have replaced the hard drive, and performed diagnostic tests on it as well as other services on it.  It often works for a little while but eventually (could be a day, could be 2 weeks) the problem reoccurs. Has anyone else had this problem?

[Dirk7]

Sorry, I should have proofread that passage before posting. I hope that it makes sense.