Hi there, I know this is quite an outdated thread. But still, I wanted to share what worked for me.
I noticed I had this same issue quite a few hours ago. So I started researching and I found a possible answer, if not The only.
This is what made my day:
Just press the start button and type msconfig.
Once there, in the Boot tab click the Advanced Options button.
In the window that pops, go for the upper right and there should be a checkbox, just make sure to leave it UNTICKED.
Click OK in everything you opened, save your work and restart.
Now you should be able to see your whole 4Gigs available in System Properties.
NOTE: That option seems to be quite useless whatsoever. It just seemed to be reset to 0 (Zero) every time you reached that window so just make sure you don't tick it again.
I hope it helps future PC users.
Have a nice day.