first off, are you sure you're not overloading the UPS?  I've had fairly good luck with APC in the past, though I'm sure it can vary.

 

Ignore surges and storms for a second and try this test.  With your computers and whatnot plugged into the UPS, unplug the UPS from the wall.  See if your computers remain on.  If they don't, you need a more powerful UPS.

 

My current desktop is running off a cyberpower UPS -- no complaints though I don't have many power events around here.  It's not that fancy though it does have AVR -- though unlike some APCs, you can't manually adjust the exact values at which the unit will switch the battery.

 

Secondly, press F2 at the dell screen to enter the bios.  Many if not all dell systems have an option to turn the system on at a given time during the day.  Having the machine always turn on at midnight might help if you need it running for days when no one is around.  Wake on LAN might be enough option to look into.

 

Lastly, this isn't really the correct board to post this on ;-)

check the APC docs and software as well.  some of their units will let you tighten the range of acceptable incoming voltage before the battery kicks in.  the negative to this is that you use the battery more often and decrease its long term lifespan much more quickly.  the postive is that you eliminate more spikes and troughs.

 

I would also contact their warranty support and see if they can help you.  It's definitely not normal behavior for a UPS.

I couldn't figure out which board to post to. This seemed the closest.

 

As for the test, I'm out of town. But I've effectively done that numerous times when shutting off the breaker on that line. The condition ONLY occurs during storms and it doesn't seem to mattter if it's just the PC or if every slot is in use.

 

I'll check the bios. With any good luck maybe that will fix it.