What would cause beer NOT to carbonate?

I had two more of the litre bottles left of the Mr. Beer brew I did and decided to just drink them. I took them out of the closet and the bottles were soft. NOTHING like the other that were rock hard. I put them in the fridge for a few days and still nothing so I opened one. Flat as the day it went in the bottle. No fizz sound when opened and no carbonation at all. What would have caused this? I mixed the corn sugar in boiling water and then in the beer.

Not long enough conditioning
Uneven distribution of priming solution (some bottles too much, others none)
Too cold where they're fermenting
WAY too hot where fermenting
...

Since the others sound like they carbed normally, I bet it was a poor seal on your bottle - especially if it was a screw top.

DocScott said:

Since the others sound like they carbed normally, I bet it was a poor seal on your bottle - especially if it was a screw top.

Click to expand...

That is my guess too...

it was the brand new tops though and they were a ***** to get off.

Being a ***** to get off doesn't mean they were sealed well. I vote for the seal was not tight.