My guitar is already more than 5 years old. It has an endpin which I have never actually used. I bought audio jack and connected it to pc via microphone output. Sound is so unstable that I gave up on this idea quickly. So I was wondering, what is causing this problem, cables, pc output or guitar endpin. If I buy guitar combo is it possible that there still will be a problem with sound? Or most likely directly connecting it to combo will fix the problem.
It sounds to me like the most efficient way to find the defective component is to figure out a process of elimination by substituting out each component starting with your connecting cable, then try plugging into an amp. If it works fine there then suspect the interface or computer. If it still doesn't work right then suspect the guitar and its parts, depending on your skill level, you may choose to continue the process of elimination by attempting to bypass each component in your guitar, or you may choose to take it in and have a repairman fix it for you.