Based on the wording of your question I'm guessing you have a problem with enabling Hyper-V. Even if your computer is SLAT capable, you still need to enable it along with DEP and hardware-assisted virtualization in the BIOS like Goran said. This procedure is slightly different for AMD and Intel computers. The full information is here in the "Enabling BIOS settings required by Hyper-V" section.
http://msdn.microsoft.com/en-us/library/windowsphone/develop/jj863509(v=vs.105).aspx
Also just to be sure you don't actually need 4gb of RAM :). I only have 3.
IF you have gone through this whole procedure, sometimes you will still get an error that you are not part of the local Hyper-V administrators group. Just click retry and enter the admin password and everything should be ok.