Headphone impedance and line input impedance are different. This may have been why you cooked your sound card. However it shouldn't effect your monitor

One last thing to try.

Move your amp as far away from computer as posable and try to get them back to back so that the speaker is facing away form the monitor which is facing way from the speaker.

Turn the volume on your guitar right down and plug everything in. Arm your track (keeping your volume down) so that IF the volume were up you'd be able to hear it.

Turn any fluorescent lights off, turn your monitor off and turn your guitar up.

If it still sounds like crap you may want to get a new sound card.

If you are serious about recording you may also want to get a second hand POD v2. it will cost you about 100-150 buck on eBay and wont fry stuff. It will also sound great.