1. More information would be helpful. See
herePlease also include the make and model number of the monitor. Onboard video (integrated) or separate video card?
2. As you startup your system, when does the monitor start saying "Power Save Mode"? If you press any keyboard keys or move the mouse, does it display correctly; even if only for a moment?
During the startup process, is any information displayed correctly on the monitor? When and what?
3. Have you tried booting to Safe Mode?
4. Does your new monitor work well on another system? Does a different monitor work well on your system?