There's always the possibility that the priming sugar wasn't mixed thoroughly. If it's a higher gravity brew it may take longer to carb up than a normal gravity beer. I hate to put it forth as a possibility, but the priming sugar may never have been added in the first place. I've heard of it happening to others and it's very nearly happened to me a few times. If it's been stored at say cellar temp, it may be taking a little longer to carb. I don't know, 5 weeks I'd say there would be at least some carbonation, regardless of storage or gravity. Give it a good, vigorous pour and see if you can't get some CO2 out. Let us know what you find out and we'll know where to go from there. Cheers!
EDIT: inhousebrew beat me to the reply