I can't seem to get my flash sync higher?

I own a nikon D80 camera, and just opened the full menu, well I went to number 24 I believe on my camera and it said sync speed so I clicked 1/80th of a second, now I can't go higher when nikons are supposed to go 200th of a second, how do I change this? First shot or 2 it will go high but after that it will go back to 1.80th of a second, I shoot in manual so obviously switching to auto helps that

Have you read your owner's manual about adjusting your shutter speed manually? All the details are there if you'll bother to read the book

Perhaps if you go back to custom setting 24 and change it back to 1/200th, your camera will cooperate with you.