PC Ram limited to 3G's while 4 are installed, why?

I have this problem for years, but now when I host the server actually my ram isnt enough. When I say my ram I mean 3 gb, not 4 even if my pc has installed 4 on it :/

So here is a screenshot what the PC tells me -> http://img5.imageshack.us/img5/7925/pcram.png

The problem is that witht he server runned I god statistics from the task manager like thse ones: http://img88.imageshack.us/img88/7232/processor.png

As you can see my ram is overloaded :/
The processor is going down too, but his still Ok. I have to run photoshop and something else to make him glitch.

Sooo... I was wandering can you please help me how to unleash that 1 gb of missing ram?
I know this is not a hardware forum, just hoping you are gonna help me like collegaue
Thx

p.p. For all the people that checked out the screeshots I let my desctop reveal on you like a price

 

well, the problem are drivers and hardware sometimes need 32bit address space.. so that most motherboards map address space below the 4 gb barrier to the higher addresses 4- x GB. the amount depends on the motherboard, take a look if you can change the value in the bios. My server motherboard for example took 1,5 GB below the 4 GB area as it had a lot of hardware. I don't know the correct setting in the bios but perhaps somebody else can help there if you post the motherboard.

 

x32 OS can only use 3 Gb, install an x64 os and it will use the full ram.

 

Pencil did you check the screenshots?
It says that I am running x64 Win 7.

Installed Everest and checked the mainboard - Asus P5B

 

He may not have made it to the left side of the screenshot.

 

Don Redhorse has it right. If you can't find the bios setting for it, post your motherboard model number and someone can walk you through it.

 

Either BIOS, or PAE is turned off.