|Make and model of mboard???|
ATX mboards are always powered in some places even when the computer is not running.
Did you unplug the AC cord to the case or switch off the AC power to the computer when you were fiddling around inside the case?
If you didn't, it doesn't take much for you to kill the power supply or do some other damage. If your power supply is a decent make, it has protection built in that disables it from turning on for a short time when a problem is encounted - it will start up again when you have fixed the problem e.g. after 15 minutes or longer. If it's an el-cheapo it might be dead.
Are you SURE you installed the ram the right way in the slots and that the modules are fully seated?
See response 2 in this - make sure the modules are properly seated:
Are you SURE the ram is compatible with the mboard? In the worst casesof incompatibilty, the mboard WILL NOT BOOT when the ram is installed.
It is easy to test for whether incompatible ram has caused your mboard to fail to boot, or it's caused by another problem.
Make sure you have a speaker or speakers or the equivalent connected to the mboard so you can hear mboard beeps (see your mboard manual if you need to).
Remove the AC power to the case/power supply.
Remove all the ram.
Restore AC power.
Try to boot.
If nothing else is wrong, you will get no video but you will hear a pattern of beeps that indicate no ram is installed, or a ram problem.
E.g. for an Award bios or a bios based on one, that's often a beep of about a half second, silence for a half second, a beep of about a half second, silence for a half second, continuously.
"I have an 800 watt power supply and have had sortages before."
What do you mean by that?
You probably don't need anywhere near that much power unless you have 3 high end video cards installed.
Failing power supplies are common and can cause your symptoms.
Check your PS.
They often partially work, fans and hard drives may spin, leds may come on, yet you get no video and the mboard will not boot all the way.
See response 4 in this:
You might have knocked something loose when you were fiddling with the ram.
Unplug the case/power supply.
Power off your monitor.
Check all the connections of the wiring to make sure they are all the way onto their pins and into their sockets, especially the main connector from the power supply. The wires close to the mboard going into the main connector/socket should be more or less perpendicular to the mboard surface rather than at an angle. Make sure all cards in slots are all the way down in their slots.