XPS 435MT no longer powers on

My XPS 435MT will no longer power on. It powered on earlier today but could not establish an Ethernet connection to my router. A post on another forum led me to shut down Windows and then unplug the power cord and Ethernet cable from the back of the case. About an hour later, I reconnected the cord and cable; then I pressed the power button. Nothing happened; no fan movement whatsoever. The green diode next to the AC port is lit; opening the case reveals that the yellow diode on the motherboard is lit, too. I unplugged and then re-connected the power cable from the back of the case, numerous times, with no change. I made sure that the two visible connections between the power supply and the motherboard are seated properly.

Does this sound like a power supply failure? If so, can I buy a replacement power supply?

UPDATE: I found a very similar thread; unlike many of the posters, however, the fans in my PC do not move--not even slightly. Dell Support tells me that they no longer stock replacement power supplies for for XPS 435MT -- so I am purchasing a Corsair CX500. I am a bit concerned about a few of the final posts in the thread that mention having to first remove the CPU heat sink...and then having to replace the thermal paste. I'm not at all comfortable doing that!