I might try reseating all the cards, (memory, video particularly). If that fails to wake the beast, then try reducing down to the motherboard, CPU/HSF, power supply and the onboard speaker. From here you should start beeping when power is engaged. If not, one or more of the four is bad.
I've been a lifelong Mac devotee, ever since that first beige MacPlus twenty years ago. I always swore I'd never buy a PC since I loathed 'Windoze' But a couple of months ago I finally broke down, as I found I desperately needed a PC running windows for some apps that were never ported to the Mac. So I picked up a cheap but reliable NetVista desktop P4 running Win2. Great little machine, that started me slowly reconsidering the PC world. All was fine until I decided I wanted to upgrade, so I bought a bigger hdd, XP - and promptly got stuck on the damned admin password. I phoned the previous owner who basically went, 'huh?' and then went off to the IBM help page who informed me that I needed to do some strange thing called 'CMOS Rom Recovery/boot jumper' and told me what to do, I promptly did it, and everything died.
Now, when I turn on the computer the power is on, the keyboard flashes for amoment, I can hear the DVD whirr away, and the hdd spin for a few moments, then go quiet. I see the little orange light on the system board. The green power on light is, well, on. But, there is no beep at startup and a blank screen! And yes the monitor works fine, I've tested it on my other computer. I've followed IBM's instructions, disconnecting everything, checking all the pins are fine, etc.
The one thing I did do wrong though is that I misplaced the jumpers when I tried to do the ROM recovery - basically I put them on the wrong pins the first time idiot that I am. Question is, what should I do now? Should I give it up, buy a new system board? I have no idea what I should do next and I'm in desperate need of help/advice/handholding since I'm close to throwing the damned thing out the window. I know there's a chance I've fried the motherboard *groan* but I've had my grubby little fingers in it all day, changing cables and fiddling around, dunno why it would suddenly fry on me.
Dammit, the Mac isn't like this! It doesn't ask dumb questions about passwords when you do a clean install, or force you into idiotic BIOS. Installing is a snap, maybe all my prejudices *are* justified
PS. Sorry for the lengthy rant