Unless I'm missing something here...
All you have to do is turn the PC off. Either with the switch on the front, or a switch on the back (if there is one), or even unplug the PC from the wall.
On the next bootup, if you still have a prob getting into windows, keep tapping F8 until you see the boot menu. Choose Safe Mode, and then disable the Screen Saver until you can see what the problem with it is.
Oh- maybe you are talking about the "Logo" screen that sometimes appears as soon as you power on the PC?? You can usually disable that screen in the BIOS setup. Check your emachines manual on what key to press to enter BIOS setup. Or, sometimes the key is shown briefly onscreen after you hit the power switch.
Good luck,
Donk