I had a friend bring his PC to me with the same symptoms. Power on, fans spin, and that was it.
It was an HP desktop, and it turned out that it needed a new motherboard. Upon close examination, several capacitors on the mobo were bulging.
To troubleshoot, I hooked up a spare power supply, and tested the RAM one stick at a time, but no go. I was lucky to be able to locate a reasonably priced refurb mobo on eBay for his model (out of warranty, and out of production).
In this case, there were no beeps, no POST, nothing on display. So the damaged board would not even load the BIOS.