Same problem here. Monitor goes into power saving mode just before the login screen appears.
Fresh install of 32 bit Windows XP Pro with SP/3 and the latest drivers dated Feb. 20, 2009 did not resolve the issue.
My card is the SAPPHIRE 100265HDMI Radeon HD 4830 512MB Driver package: 9-2_xp32_dd_ccc_wdm_enu_75974
I was able to get the drivers to load successfully one time (after restarting from a safe mode session) and that appears to have been a fluke- the problem reappeared with the next reboot.
Any help would be appreciated.
GIGABYTE GA-MA790X-UD4 Motherboard
AMD Phenom 8650 Toliman 2.3GHz Socket AM2+ Processor
G.SKILL 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 1066 memory
Rosewill Stallion Series RD600N-2SB-SL-BK 600W Power Supply
No over clocking has been performed on the system, all stock settings.