I have an 01 Jetta that will not start. I just had a new battery put in 2 weeks ago, yesterday it would turn over and then start but bog down and die. I tried four different times through out the day and by the end of the day it wouldn't even turn over. It has been very cold here (subzero temps) so that may be playing some role but that shouldn't be the entire reason. HELP PLEASE!!!

Vehichle Info
2001 Volkswagen GLX VR6

Battery will not take a jump, I added 2 bottles of Iso-Heet (in case of water in lines)

Thanks