Do you guys think the htpc psu is not getting up to voltage quick enough and that's my problem? Would it be better for me to use a 7805 off the 12V rail and create my own 5V rail to work with?
If that is basically the only thing that changed as far as connections go, I suspect that may be part of it. It sounds like the rest of your circuit is the same except the new power supply, so I suspect the new power supply. Try using a different power supply.