No sound when connect guitar

You must connect a short jack cable between the GK2 or GK3 and you normal guitar jack out. Secondly, the switch on the GK should be in the middle, that will give synth & dry guitar simultaneously.

Have you checked a different cable?. Also, when you plug in the unit, there should be a "pop" if everything is turned on. If there isn't, the connection is bad someplace.

You must have the matching input jack and connecting the guitar cable to the amplifer INPUT and selecting the source will let you play on the guitar.
Check the cables and see they fit correctly.

Many try to use poor quality guitar cables and have the problem. The sleeve of the guitar cable plug turns on the battery in the guitar. Always loop the guitar cable through your belt or the guitar strap to avoid the cable wisting the plug in the guitar causing noise and WEAR that wears the plug sleeve to the point it no longer will activate the guitar.

If the guitar is active and the battery is dead you will not get any sound. If the output jack or some of the controlls have been twisted and may have broken the connections on the inside.

Make sure you have the correct power adapter, not a substitute. Make sure your guitar is outputing enough... You LIKELY will need a guitar that has a preamp in the guitar, (not a passive pickup guitar). This device is nothing more than a small amp that drives a speaker which the sound travels up the hose. If your guitar creates a buzzing noise, then this device will do that too... Plug a set of headphones directely into your guitar to verify the sound is clean... NOTE, only one side of headphone will have guitar in it if the headphones are stereo type.

It sounds like you have NOT connected the power adapter to the box to power it. The guitar sound won't be too loud as you run the hose to your mouth and pick up the sound with a microphone such as a Shure SM57 which then goes to your amplifier. Without the power adapter the internal amplifier will not produce any output.

Yeah, sounds like a bad connection. If you are handy, you can take the jack out yourself and determine if it is a loose wire or solder connection. If everything looks fine then you should squeeze the connections togather inside the jack itself. Sometimes it just gets pushed apart and does not hit around the male end secure enough.

OK... Most of the guitars have a PAINTED on shielding in the well with the electronics. Sometimes the electrical connection to this is broken causing hum. Sometimes the connection is by way of the potentiometer shaft nuts and they spin and break the connection. This paint is conductive and often black know as aquadag. Use an ohmeter to verify connection.

While it could be true that you're having a problem with the guitar or cable as the previouse expert suggested, to say that it can't be anything else is false. It could be a jack problem...it would only be apparant when the jack is making contact with a cable. I do think you should test it with another guitar and another cable but if that is not solving the problem then I bet it's a problem with the input jack of the amo itself or even one of the ionternal components (this is a digital amp and there are MANY components and settings that can trigger a problem like this) If the problem is not solved with a new cable/guitar configuration then it's time to take it to the shop.