Computer Won't Boot

I have a custom built PC:

-ECS K7S5A Motherboard
-AMD Athlon 1800+
-Geforce 4 TI4200
-512 Megs PC2100 Memory

The problem is I will turn my computer on and I don't get any system beeps and no picture on my monitor. It boots up the hard drives and disk drives fine. I have tried the following:

-I switched out my motherboard and processor (For brand new ones)
-I have exchanged the memory for some older memory
-I have tried a different video card
-I have unplugged the hard drives
-I have tried a different power supply (Brand new one)
-I have plugged it into a different wall outlet
-I have tried a different (working) monitor
-I have unplugged everything from the motherboard

I think that pretty much covers everything I've tried, and I still get the same end result. This is getting very frustrating...and I have looked up many others with the same problem and I can't seem to find out what is wrong with it. The thing is: if I play with the power and restart switches long enough, it will work fine, but now I can't seem to get it going at all. Please help...

I guess I should also add that when I DO get it to boot up, my BIOS settings are reset...

try a new cmos battery

Well, I switched the motherboard and that didn't work so I doubt it's the CMOS battery...any chance it might be my tower...I know that sounds strange, but whatever

reading over your post looks as though you have pretty much covered the bases, did some reading on back in the forums here. some have found case fans, cpu fans, keyboards, the mouse to have caused problems, and this is all possible, the case would only be a problem if a riser was not in the correct place or the board touches other components. i could tell you to try a few more things, but think i would be going over what you have allready tried. if both the boards came from the same source, and were both mfg. together they may both have defective cmos batteries, just a thought from a insane mind.

Well, I took it to Fry's to see if they could fix it. A few days later the guy says it's my motherboard...So I said that I would buy a motherboard and have him install it, and if it didn't work he would have to fix it. So this time I got a different brand of motherboard and tried it out to no avail. The guy said he would keep it and figure out what's wrong with it. (Though I doubt he will be able to)