Im confused, I thought I had my BFP...?

Ok, so. I took a HPT today and I saw the plus sign (looked like this +|), though it was very light. It started fading and now I only see the vertical line (now it looks like this | |) that was left over from the plus sign. I thought it was a BFN but when I looked on the box it said that a negative result would be a minus sign(supposed to look like this - |)... so I'm confused, what happened to the other half of the plus sign? Am I pregnant or not?