PSU + 2 Video Cards = Please help

Hi everybody, new here. I have a handful of Dell Optiplex MTs, 2 x 755's and 2 x 760's and some others. They have the 305 watt PSU in them. My systems have 2 SATA drives, 2 optical DVDs, a single Duo Core E8600, and 4 gb of DDR2. I have added 2 cards to the systems and am having blue screen and freezing problems. The first, in all of the machines, is a Canopus FIRECODER encoding card (DV-Firewire input only). It is a PCIe X1 card, and takes a molex plug from the psu. The other card (which doesn't seem to matter since I've I tried a few models and makes) is a graphics card (NVIDIA 8400 or FX5200 or Radeon series).

The computers only bluescreen or freeze when we capture DV into the Firecoder card. Sometimes during capture the audio gets choppy, like a buffering issue when watching a webstream. Other times it crashed 4-5 seconds in. Some of the recordings go for 2 hours straight.  I have reinstalled the cards, drivers, and set my Dell config to only run off the nvidia (or ATI cards I've also tried) and not the onboard display adaptor which I know can be an issue with the Firecoder. Everything works, except when capturing through the card. I've talked to Canopus, they have had no conflicts with Dell's recent motherboards, etc. Dell was no help at all over the phone.

Having eliminated a lot of variables, I now think that I do not have enough power to run 2 SATA HDs, 2 Opticals, Duo Core chip, large heat sink/fan, and 4 gigs of ram, along with a Video card and an Encoding card. Would a lack of power cause a freeze or bluescreen during video encoding? I know I shouldn't be using Optiplex's for this type of hi volume, video intensive, work. That aside, please help me out, send some advice, got any ideas, etc??? I'm convinced it's the power now, what do you think is the problem?