Problem with ECS-K7S5A when upgrading to DDR

Here's my problem - I've had this board since December. My system has been running flawlessly (Really!). I decided to upgrade my PC133 393 MB SDRAM for a Samsung 512MB DDRAM. This is where the problem is. The DDR is not recognized. I get no POST, no video, no beeps, just drive lights flashing intermittently. I thought it was the memory, and traded it for a new stick. Based on other posts, I've tried the "Support" settings of "Safe", timing of 7T, etc, and that hasn't worked. It may be the PSU, but can that make that much difference when the other thing I've changed is the RAM? I don't want to go out and spend money on a new PSU if I don't have to. I've called Support twice and all they can tell me is to try and re-seat the stick, and clear the CMOS, and they will have an engineer get back to me. Guess what? I haven't heard a word. So I'm asking you, what is the problem? And yes, I took out the old memory before putting in the new memory because I know the SDRAM and the DDR won't work together. PLEASE HELP!!
My system:
K75SA with Athlon XP 1700 and volcano heatsink
2 HDDS - 1WD 40G, 1 Maxtor 20G
1 Iomega CD-RW
1 LG DVD-ROM
ATI All-in-wonder 32MB AGP video
300 PSU - AMD approved
Windows Me

try booting it with just the necessary attached (psu,memory,cpu & gfx card) see if it will post, if it does then the problem is likely to be the psu.. if it still won`t post then maybe you have duff slots on your mainboard for your ddr memory