Whats wrong with my pc?

Hi guys i need to get to the bottom of this problem on my pc, i can start my pc and reboot it no problem but if i go to start/shutdown then press the power button to start it up my pc starts but i cant see anything as my monitor doesnt go out of standby, what i have to do is turn pc off by holding the power button then pressing the switch on the psu off then on then my pc starts ok, i bought a new battery for my motherboard but that didnt do it ive also had to take 1 of my memory sticks out as for some reason my monitor wount go out of standby with one, ive tried both stick and 1 was causing problems so at first i thought it was the memory stick but its not as im still having the problem however if i put the stick back it wount go out of standby strange how i got this problem at the same time maybe its the motherboard? ive tried a different gfx card and no luck so what can it be? PSU, CPU or Mobo? im baffeld by the fact i can restart my pc i can even put it to sleep or hybernate and i can wake the pc up from that but i cant shut it down if i do i have to turn psu off/on, according to the manual that resets the RTC parameter or something like that, sorry for the long message hope someone can help.
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Asus P5K-E WiFi
Intel Core 2 Quad Pro Q6600 "95W Edition" 2.40GHz
Crucial Ballistix 2GB (2x1GB) DDR2 PC2-8500C5
BFG GeForce 8800 GT OC 512MB GDDR3 HDTV
Samsung S86 26" LE26S86BD HD Ready Widescreen LCD TV
2x250GB Western Digital RAID Edition SATA-II 16MB Cache
Samsung SH-S203NBEBN 20x20 DVD±RW Dual Layer Serial ATA
Thermaltake VA3000BWA Tsunami Dream SuperMidi Aluminium Tower
Coolermaster Real Power 620w Modular Power Supply

Have you tested another PSU on your PC? seems like a much more complicated issue that could take a complicated solution, so why don't you try with another PSU to discard it? since you've already tested the ram modules, and by "tested" i mean "did you check them with memtest86?" at least 8 passes for each one of the modules in every single slot on the motherboard.. post back with results, please :)

brianzion said:

Perform a SFC Scan

1. Click Start, click All Programs, click Accessories, right-click Command Prompt, and then click Run as administrator. If you are prompted for an administrator password or for a confirmation, type the password, or click Allow

2. Type the following command, and then press ENTER:

sfc /scannow

A message will appear stating that 'The system scan will begin'. Be patient because the scan may take some time

3. If any files require a replace SFC will replace them. You may be asked to insert your Windows 7 DVD for this process to continue

4. If everything is okay you should, after the scan, see the following message "Windows resource protection did not find any integrity violations"

5. After the scan has completed, close the command prompt window, restart the computer and check.

more information here How to use the System File Checker tool to troubleshoot missing or corrupted system files on Windows Vista or on Windows 7

Hi and thanx for helping but the problem isnt with windows its hardware or possibly bios, when we turn our pcs on its the bios that comes first, i dont have a spare psu but i will see if anyone has.