I installed 3x4GB ram and a new SSD disc but now the computer is saying 12 gb but only 4 is usable. Tried you tube with the settings on windows like boot settings and stuff but to no avail. anyone help.

Could be a lot of things:
Ram compatible with mobo
Some ram needs to be purchased and installed in pairs.
OS 64bit?
Update bios
Ram fully seated
Maybe those slots are bad. Try moving the original ram to see if they work.
Read the mobo manual carefully about the ram.

Cheers Pete , updated Bios, sorted settings it sees there is 12gb ram but says 4gb usable in brackets. Checked and they are seated and cleaned. 64bit system.
Emailed gigabyte they say use original windows disc and save all work and see if that helps ?

Activate your XMP profile if you're using XMP certified memory. Clears up most of the issues.