Short version: they looked a lot more like 
than 
. Most accounts of Vikings that are contemporary of the centuries where shield-Danes and spear-Danes went "a-Viking" describe distinctly hygenic people that bathed and took care of their hair (and wore it long).
EDIT: I thought I could have a little fun with a very loosely associated Beowulf reference to Danes (and even more loose associations with Geats therein too) but I got the 
experience for doing so. 
They didn't have Hitler Youth fades with lazy and sloppy beard fusions. Period. Full stop. Stop doing that. Looking right the fuck at you too, P R E S T I G E T V. 
Shaved at the back, front left long to chin/shoulder length, parted at the center and pulled into two ponytails to hang along the temples, sometimes pulled into a topknot instead. Possibly braided, but definitely adorned.
It's a very common warrior hairstyle accross Eurasia. But it isn't very attractive to modern sensibilities.