4 gigs available or 4 gigs *total* ???
Probably not telling you anything you don't already know, but Windows will need part of that 4G RAM along with any startup stuff & bloatware. For example, my desktop rig has 16G but Windows 10 takes up memory, then stuff like-- itunes helper, Steam, Dropbox, and bloatware-- Apple Update, Acrobat quick launcher & everyone's auto update service.
Have you tried stopping some of the optional services to free up more memory? May or may not work.