Also, read the other day that somehow you could preset volume levels between trailers/print with the CP500. How?
Basically, you assign a particular format and fader setting to one or more soft keys and have the automation pulse between them. If your automation is set up to pulse multiple soft keys, you can set the default format to be at a low volume for trailers and then have a sound cue at the start of the feature that selects another format (both can be "Dolby SR," but the second one can have a higher fader setting) at feature start.
If your CP500 firmware supports "auto-digital" and you have the SRD cards and reader, there's an issue if you have two formats with the same name--it's pretty much covered in the earlier thread and there are at least two workarounds for it.
The other alternative would be to use Brad's remote-fader trick (see the "tips" section of this site), which works on all processors but usually requires reworking the automation system.
I'll suuggest that your backup power supply took the proverbial dump a long time ago, and you didn't notice it until the main power supply died.
If you're sure they both went at the same time, I'd check the AC line voltage where you're plugging them in and make sure its correct. I suppose one power supply leaving you in a catastrophic manner could potentially take the other one with it, but the most likely scenario is that your backup was already pooped.