Note: Not emotional problems, although sometimes it makes me want to cry...  ​

Since building my new computer a couple of months ago, I have been running into constant problems, I've built a PC before so I knew exactly what I was doing throughout the whole process, but so many things are going wrong and I don't really know what to do about them...

Specs:
Windows Vista Ultimate

1x ASUS P5N32-E Motherboard
2x Corsair 2GB DDR2 RAM
1x Intel Core2 Duo CPU (2.4GHz)
1x Albatron NVIDIA 7800GT GPU (Piece of shit, I know, from my old computer)
1x WD 500GB Internal HDD


Problems:
Main problem off the rank is as follows; every time I turn the PC on, nothing happens, the PC turns on but the boot screen never loads up and my hardware doesn't detect that the computer is functioning (Keyboard off, Mouse off, Monitor gets no signal input).
Luckily through blind luck I found a way to sort of rectify the problem, (although not remove it completely); and that is to lightly push down on the corner of the motherboard where the wires connecting the power and reset buttons to the mobo are located, I have to hold my stance for 8 seconds before I get a single beep sound to signal that its starting up.
Believe me, it's not fun to do that every time you want to go on the computer, but just wait, it gets worse.

Secondly, 5 minutes after the first startup the computer will have one of two outcomes.
1) The whole thing will freeze in place, meaning the mouse arrow along with everything else is frozen.
2) BLUE SCREEN OF DEATH, signalling the same old IRQL_NOT_LESS_THAN_OR_EQUAL thing.
Now I know what you're saying, it all points to a RAM issue, right?
But I've tried removing each stick at a time AND placing them in different slots but I keep getting the same problems happening.
My computer shows in the properties that I always have 4GB of RAM and 2GB when I have one removed so I don't quite understand what's wrong.
However after that happens, I press the restart button, then I have to press on the motherboard again for 8 seconds, then after that it will run flawlessly up until I switch it off again, then the following day when I turn it on I have to go through the whole process.

Third, just recently (more specifically after buying a new television) a lot of my USB ports are starting to fail, more specifically to do with my 4-port USB hub and my 500GB External HDD, unplugging them from the USB port or swapping them to another USB port doesn't work, I have to disconnect their mains power supply first, then wait and reconnect it again, and even still it sometimes only works after swapping to a different port as well.

IT IS FRUSTRATING BEYOND BELIEF.

I don't want to sit there for 8 seconds pressing on my mobo, then waiting 5 minutes for the fucking thing to freeze up on me so I can restart it; (I neglected to mention that it will freeze up again if I decide to restart it earlier than the initial freeze, it's sort of like it has to do it or something), then pressing the motherboard for 8 seconds, then wasting 10 minutes trying to work out how to get every fucking USB port on my PC to work properly.

I have had enough

I want the most cost effective measure of rectifying all of these problems, and would prefer to spend NOTHING moreso than spending SOMETHING.

PLEASE help.

I'll give Rowain's method a try first, however since I'm not home I won't be able to test it for a while, secondly I'll try the lithium battery method since it was what I was going to do first but shortly forgot about.

Third, my PSU is more than capable of running my computer and all the components since I had to make sure of it, and things ran perfectly upon initial construction of my PC, it's just starting to die now.

I am in STRONG consideration of reverting back to XP, however I am very used to (and comfortable with) how vista functions now and would prefer to avoid it.

Thanks for all your help guys, I'll give it all a go and get back to you.
As for people that just say "It's a motherboard problem" and nothing more......... it doesn't help, seeings as there could be a million different motherboard problems.