argh, I'm too late to save you replacing the caps. Usually it's something simpler. As you get older, you're more likely to completely rebuild equipment because it is plugged into a faulty power point.
That beeping is normal, it's the UPS's way of saying there is a power failure. Most of them do it, and you can download a pdf user manual from the net and find out how to tell it not to do that.
The other thing I would suggest for this would have been to charge the batteries on a different charger then try it, being careful that it can make lethal power on it's own.