Bad PSU, or bad PSU tester?

When I turn my computer on, the light and fans in the PSU come on, and an LED on the motherboard comes on (the +5 V Standby Power Indicator LED), but nothing else happens.

So I bought a Coolmax PS-228 PSU tester. I plugged in the 24 pin and 4 pin (CPU) connectors, turned on the power, pressed the ON/OFF button on the tester - and there is nothing on the tester's display at all, and no beeps.

To anyone familiar with the PS-228 - should I expect at least something to display, or should I hear a beep? Or could the PSU be so dead (even though its light and fan come on, and the mobo LED comes on) that the tester would do nothing?

Thanks for the response.

Yes, I did hold the power button down. I just kind of assumed I'd see or hear something to tell me the PSU was bad.

After I posted my message I tried a few more times, and noticed a lamp that's plugged into the same power strip as my computer flickered just slightly when I pressed the tester's power button - and I'd noticed this same thing happening before when I pressed the computer's power button after it had failed, so I began to suspect the tester was OK and the PSU was broken.

It only took me a couple of hours to realize I could test the tester on the PSU of the computer I'm typing this message on, my 10 year old Dell Dimension 8200, which somehow continues to chug along. I tried it, and the tester worked fine, so the PSU in my newer computer is bad.

What, by the way, does the 5v standby light indicate exactly?

Thanks for your replies. I bought a Corsair TX650M, spent the day replacing the psu, the motherboard (lots of bent cpu socket pins, because I'm an idiot) and a new cpu cooler, and the system is working now.