We'll the RAM was an adventure but probably turned out to be one of the more esoteric problems I've fixed. Surprisingly quick too.
My board is a x58 board with triple channel RAM options. I did the following:
1.BIOS was recognising 4gb of RAM
2.Changed out the 3x2gb sticks with my old 3X1gb sticks. All RAM checks out ok.
3.Put the 3x2gb RAM in the other ram slots. Board posts as 9gb but Windows says only 3gb usable.
4.To Google - See something that says to see if the RAM is being limited via the Mscofig boot advanced options.
5.Check Msconfig but I cannot select the advanced option and there is no default OS displaying in the Boot screen.
6.To Google - Go to Manage and Disk Management. Apply a drive letter to the 100mb drive. Reboot.
Windows must have artificially limited the RAM to 4096 even though the option wasn't checked. I wonder how long it has been liked that. I probably just checked the Post screen to make sure all the RAM was recognised when I purchased them.
8.BF3 Profit? I'll check to night to see if the RAM makes a difference. I'll also need to keep and eye on the system stability. All the RAM has the same timings but the manufactures and sizes are different. I've tried to limit the impact by have 1 triple channel as all 3x2gb stick with the same manufacturer and the other triple channel with 3x1gb sticks with the same manufacturer.
Will post back with results later.
Well the PC bluscreened whilst I was writing this. I think I got greedy with using the old RAM. Have taken it out and will run Memtest I think.
You don't make friends with salad