I am needing to upgrade my power supply from a 500w Ultra to 900w Antec. My system works fine with the 500w PSU but I plan on upgrading the video and including a tuner. When I connect the new Antec PSU nothing works including the fan in the PSU. Again, the system works fine when I reinstall my old PSU. I tested the Antec PSU per instructions I found on the web, and all of the voltage outputs appear to be correct. Are there PSU's that are not compatible with an ASUS P5G41T-M LX PLUS mother board. There is nothing on the board other than AMD Quad 4.2 Ghz processor and 8 GB of memory.