Why is my computer only using 4gb out of 8gb installed?

Hello and welcome to the forums
Go to msconfig>boot>advanced options and make sure "Maximum Memory" is unchecked.
Also is the BIOS reporting 4GB or 8GB ?

Do you have 2x4 GB sticks or 4x2 GB sticks installed ? If only two sticks, one may be in the wrong slot. Also check if Memory Remapping Feature is enabled in BIOS.

max memory is unchecked, the remapping this is enable, I have 4 x 2. When I put my RAM in slot 1-3-4 I have 6gb usable and when I put a RAM stick in slot 2, it's 4gb usable and my computer uses the other 4gb as "Hardware Reaserved" [Saw that in the Ressource Monitor]. Oh and the BIOS is reporting 4gb but CPUID and my computer [Right-click computer] are seeing the whole 8gb.

What is your gfx card ? If it has small memory, then Windows reserves a good portion of RAM to video. But it is interesting to note that BIOS shows 4 GB. What version of BIOS did you flash to ? What is your CPU ( it seems to be Intel i5-750 ) ? your RAM ?

I have a HD 4670 1gb GDDR3 with the intel i5-750. Will be upgrading video card to gtx 460...just need it to get here. On the manufacturer website it says P7P55D-E PRO 1002 BIOS for the BIOS version but I doubt it's what you are looking for.

I am sorry. But because you do not give the requested information, we are made to speculate. I asked information about your RAM. But you did not take time to read the whole content of my reply and give me your RAM spec.

You have the latest BIOS available.

If you have 1600 MHz RAM, then you may be better off setting D.O.C.P or X.M.P. in BIOS depending on your RAM specification. This setting increases voltages to better cope with the components. If you have 1333 MHz RAM, no need to do that.

I have Asus P7P55D motherboard close to yours. I have 8 GB 1333 MHz RAM. Radeon HD5770, Intel i7-860.

Oh sorry about that, I did read your whole reply, I just forgot about that part while writing my answer   . Yes my RAM is 1600 mhz

O.K. Have you set D.O.C.P. in BIOS ? This is required for your RAM and CPU. i5-750 and 1600 MHz do not go well together unless you have D.O.C.P. enabled in BIOS. Or X.M.P. mode depending on your RAM specification. Please read the M/B manual.

Ok so the only thing I found that could help on the RAM packaging is: PC3-12800 8-8-8-24 1.8-1.9V

Oh and I did put my BIOS in D.O.C.P and X.M.P mode and it didn't affect my usable size. [Wouldn't let me edit my previous message.

Read the i3/i5/i7 'Missing' Memory topic in the GIGABYTE 'sticky'

Also wanted to say that I found some bent pins on my motherboard around the top left interior corner. Should I unbend them myself or pay 65$ a professional to do it.

Best answer selected by Analyzerus.