#1
so i have a problem. I wanna play and record my guitar into my computer, but using my amp. I've done it before. What I did was plug my guitar straight into my amp,then, since i have a headphone jack in my amp and another cable,plug my amp into my computer.Its worked before,but now it doesn't.I dont know what I'm doing wrong this time. If anyone else has done this successfully or can offer any advice i'd really appreciate it.

P.S.
I think it might be the headphone jack in my amp, because when i plug straight into my computer it works fine.
#2
I don't think you're really supposed to do that, it can ruin hardware running an amp directly into a computer as far as I know, but if it works plugging it directly in then that must not be it.

I don't really know what to say, but you should get a proper interface to record on your computer, that's the only real advice I can give.
#3
you can run low volumes out the headphone jack to your line in on the sound card but yea if its working with a different layout you didnt break anything.

I suggest a USB or Fire Wire interface...

Line 6 UX1 or UX2 are great usb interfaces...
#4
get a interface.

AND MIC YOUR AMP.

i prefer a audix i5 or shure sm57

it will make you sound 405328450 times better
Fender H Stratocaster USA.
SX P90 Mahogany Hawk
Gibson Les Paul Studio Double Cut

Delta Labs Tube Driver
Hardwire SC-2 Valve Distortion
Delta Labs Stereo Chorus
TC Nova Repeater
Korg Pitchblack Tuner Ped

Fender Super Champ XD
#5
^How can you guarantee that, what if he's playing in a poorly treated room? Any interface you say, that would offer thousands of possibilities and I'm sure I can find one that will sound crap.

Why must people insist on going off topic with a question like this, they are asking how to fix something they had working. Not asking the best way to do something.

For threadstarter, sounds to me like the headphone jack may be gone, try plugging headphones in there as an idiot proof test, but I'm sure that will conclude that. It may just be a bad connection, that you can either fix yourself if you know what you're doing. Or if the amp is covered under warranty still just bring it in.