I've had this machine running for a few years now without any issues. It isn't overclocked or anything. The motherboard is an Asus P5QL Pro with a Q9550 C2Q.
A description of what went happened...
-Pulled the case away from the desk to show someone the heat sink on the processor.
-went to wake the computer from sleep mode, appears as if it wasn't waking (no beeps) had this issue a few years back and needed to pull the cmos battery to reset it.
-turn off the computer, pull the battery, wait a few seconds, put it back in, reboot. beeps once, pause, beeps a 2nd time, still no monitor action.
-do the above things a few times until i realized the monitor cable was unplugged from the back of the monitor. no idea how or when that happened, most likely pulling the computer out caused it. DOH!
-plug the monitor in, realize that the 2nd beep was the alert for having to reset system time and the such.
-awesome, back in business. until windows crashes on startup at desktop.
-start up machine, doesn't post. do the battery and jumper thing, restart, windows crashes on the loading screen.
-restart machine, doesn't post. still doesn't post either
in the current state, i've removed the battery and switched the jumper numerous times. i've pulled the battery (jumper in normal state) and let it sit for 20 minutes. i pulled the battery and switch the jumper and let it sit overnight (8 hours).
taking the memory out gives me the expected beep code (1 long 2 short). pulling the graphics card results in nothing different.
all fans spin up, hd seems like it's getting power. there is a light on the mb that lights up. i didn't smell anything burning.
any ideas on what else to try? i don't know anyone with an old mb with this socket. i am hesitant to just buy a new socket 775 mb (wife wouldn't understand this is a new old part, was hoping to upgrade entire pc in the next year or so).
Maybe the vga card just died? Try another vga or maybe an on-board if you have, to see if it works.
Also, i've never had this happen to me (actually once, but with a pc that was unused for years), but maybe the cmos battery died. It can happen after some years. Try replacing that. It's not expensive, it's a normal "button" type battery.
If at all possible, could you try swapping parts in another computer?
Also, it's a bit strange that the computer won't post at all, but if you remove the RAM, it'll beep. To me, that means the cpu is working, and the RAM is working. Your mention of having the monitor unplugged when you pulled the tower out (supposedly) leads me to believe that maybe the cable is damaged, or if you're unlucky, the pci slot was damaged. That might be what's affecting your lack of display. Check to see if there are pins missing, bent, or cracked plastic around the slot.