SR1000T won't power on

Hi there. I've been having trouble with my desktop for a while. At some point, I came home and tried to turn it on. Only to find that pressing the power button did nothing. Later on that day I tried again and it worked fine. As far as I can tell, when that happens, the green light in the back doesn't light and there's only a soft clicking sound from the back of the tower. I tried replacing the power cord and using different outlets, but it turned out to be by chance whether or not it would turn on. It's been a few months and the power went out a few nights ago. Normally this wouldn't last more than a day, but I haven't been able to power it on since it went off that night.

Is this a serious (and expensive) problem? What should I/ is there anything else I can do?