What will happen if I install more RAM than specified in manual?
Solution 1:
Take the confusion out of the issue. What does Crucial or Kingston say about the memory capacity of the computer?
The manufacturers manual is a snapshot in time, it only reflects what the manufacturer tested, when the manual was being written. They are rarely updated, unless a new version of the computer / motherboard / etc comes out.
Kingston & Crucial are willing to test with newer memory chipsets, etc. So if they say your model will accept more, then it should work.
I couldn't find the board on Crucial, but Kingston states:
Standard Memory: 0 MB (Removable)
Maximum Memory: 8 GB
Expansion: 4 Sockets
CPU & ChipSet: AMD Athlon 64 (AM2) Nvidia nForce 560 AMD Athlon 64 X2 (AM2) Nvidia nForce 560 AMD Sempron (AM2) Nvidia nForce 560
Bus Architecture: PCI; PCI Express; USB
Mfgr's System P/N's: N/A
Comments MODULES MUST BE ORDERED AND INSTALLED IN PAIRS for Dual Channel mode. Kingston offers "K2" Kit part numbers for Dual Channel mode.
If 4GB is installed, the recognized memory may be reduced to 3.5GB or less (depending on system configuration and memory allocation).
Maximum configurations require 64-bit operating system.
AMD Sempron processors support DDR2-533 and DDR2-667 memory only. DDR2-800 modules are not supported with this processor.
At 1066MHz, this system supports up to two single rank modules ONLY. DDR2-1066 is supported by AM2+ CPUs only.
Solution 2:
What will probably happen is that your motherboard will recognize only 4GB of the 8 you have installed. The chipset most likely can't handle more than that. You will need a new motherboard (and a 64-bit OS) to see all 8 gigs.
Solution 3:
Maybe your manual is out of date. According to MSI website this motherboard supports up to 8 GB. Athlon64 processors feature an integrated memory controller so I believe every system with 4 memory slots supports 8 GB of RAM.