Plugging a guitar output into a sound card Line-In (blue?) should work even though you’ll only get sound on Left of the stereo pair and it will be slightly weak. If you’re missing the ability to get sound into Audacity at all, it could be the wacky way Windows decided to arrange sound sources.
If you do get bouncing lights and a wavy blue line but can’t hear the work, that’s a different problem. Set Audcacity preferences for Hardware Playthrough (restart Audacity) and cross your fingers. Very few computers let you hear your work in real time and the delay/echo drives people nuts.