Understanding Memtest?

Hey guys, I am working on a DELL XPS 400 [Windows 7]. This unit has 4 slots with 2 ram sticks 1gb each, it was booting when the owner brought it but I researched the beep codes and found it is a ram issue so I reseated the ram sticks one at a time and it booted up but I am thinking one of the ram slots may be faulty as one time it did not boot up and gave the beeps again but the 2nd time it worked, does this mean it can have an intermittent problem?

Also, when the unit is on in windows it is showing the 2gb now in memtest as can be seen in the attached screenshot, it is showing CPU's Active 1, I am not understanding why it it's not showing 2 CPU's active?

Doesn't look like I can upload the screenshot here so here's a link to it:

http://i493.photobucket.com/albums/rr298/mikehende/20140717_111800_zpsa25eeb40.jpg

 

I wouldn't pay any attention to that Mike as you know you really have one cpu with 2 cores and that won't always show up properly.
I would run memtest86 for at least 1 full test or 8 passes and then run 1 stick the same way to see if there is a bad stick as that is way more likley than a bad slot.
Then if all check out you can try slot 2,3, and 4 with each stick. Unfortunately that is the only way you will know. Surprising that you don't see the 4 slots represented in that screenshot
showing what the ram is.