Originally Posted by Psyckosama
Pardon my ignorance... a starter?
Liquid yeasts generally do best with a starter. Starters also help to ensure you have a viable culture.
In general, put your yeast into a large measuring cup, preferably on a stir plate, if not you will need to stir frequently and aerate the starter well.
Add some must to the yeast slurry to the tune of 1/2 the quantity of yeast slurry you have. e.g. if you have 2 Oz of yeast slurry add 1 oz of must. Stir and aerate well for 15 minutes.
Add another 1/2 volume of must to the slurry, stir and aerate well for 15 minutes.
Rinse and repeat until you have 4x's the original amount of yeast slurry.
Let is sit until you see signs of activity, this is called "proofing" and ensures the yeast are active at this point.
Once you see signs of activity aerate the living (*^&!@ out of your big batch of must and add the yeast slurry in.
That being said, as others recommend abandon the sweet mead yeast. It is NOTORIOUSLY difficult, stalls, fails to start, produces off flavors if not carefully monitored. It's not a beginners yeast at all.
Since you already pitched once, if you decide to change yeasts you want something that aggressively kills any other yeasts it encounters, this limits you to mostly champagne yeasts. The two that tend to work the best are Lallemand K1(v)-1116 and Lallemand EC-1118.
If you can't find those Montrachet Red Star Champagne yeast will also work very well. Stay away from the Wyeast or White labs liquid yeasts (even the champagne yeasts) until you have more experience with fermentation management. While great results can be achieved it requires a bit of experience to get them to do their thing.