Laptop? Desktop? I'm not 100% sure what you are saying here....do you mean that when you boot your machine you get all the way into Windows but all you see is the background desktop wallpaper image but none of your usual icons, taskbar. start button are popping up?
OK...so on first power up a machine that used to work fine is powering up, but all you see is a black screen now. First thoughts..RAM problem (Reseat RAM, or try one stick at a time). PSU problem (swap PSU). To verify you have a no logic condition after you turn it on and wait a few minutes, try pushing in the power again to indicate that it should shut off again. If this is just a display issue and your machine is in fact running then it will see that one press of the power button as an indicator that you can't type or see the screen but that it should gracefully shut off again. If that one press does not work and it keeps running then we call that a 'No logic' ..'No POST' condition where you have a problem with one of the needed pieces to power on self test (POST). Check the easy and the obvious first