Verify your yoke us good. Check the resistance of the vertical and horizontal yoke of your old monitor and compare it to your new monitor. You want to make sure they're close to the same to verify there isn't a problem with your new yoke (broken wire, short, etc). If they're good odds are good that you've either put a cap in backwards, bridged something with a glob of solder, have a broken trace going to a pad, or one of the parts has separated from the pads and isn't making connection anymore.