If there are no diagnostic beeps or lights, the easiest and one of the most common things to find is a problem with the video card.  Make sure the card is plugged in completely( if you have a card) and make sure the monitor cable is completely plugged in at the monitor and computer ends.  Can you see if your monitor works with another computer?

ppost

If you are comfortable working around computers, you could try the following:

Note: The only 100% method of testing a PSU, is to install a know working power supply.

Unplug the cord from the power supply, hold the power button in for about 15/20 seconds, open the case, unplug the 20-pin power connector from the motherboard and jump the Green wire to one of the Black wires, reconnect the power cord and power the system, if power supply's fan and the hard drive runs, then the PSU should be good.

Note: Do not remove any wires from the plug, use a small piece of wire or a paper clip as a jumper.

Power supply checks out and the system still does not work, again remove the power cord, hold the power button in for several seconds to discharge the residue power, reconnect the 20-pin connector to the motherboard.

Remove all the PCI cards, the video card [if applicable], memory, all peripherals, disconnect the data and power cables to all the drives, check that the front panel cable is connected to motherboard, with nothing else connected to the system, reconnect the power cable and power the system on.

If you do not get any beep codes and there is no change in the diagnostic lights, then it would appear that the motherboard has died.

Bev.

I had a similar problem with my 2350: pressing the power button started up the fans and the lights but the machine would not boot. I am not sure if it is the same problem you are experiencing, though.

I fixed it by unplugging the machine from the power source, waiting for the mainboard LED to go out, resetting the CMOS via the mainboard jumper, and removing a memory DIMM. I then plugged it back in, rebooted and got video, and entered the BIOS (F2), saved, exited, turned off the machine and disconnected power, and replaced the DIMM I had taken out earlier. I plugged the machine in again, booted back into the BIOS, and saved and exited. Problem solved.

The problem seems to occur when the machine loses power partway through a boot or shutdown. I think it could be CMOS corruption, but I am not sure.

It was easy enough to fix, but I had some bad moments, especially when it seemed that my expensive GSKILL 1gb DIMMs were damaged. They were not -- whew!