Make sure you have your input trim turned up and you have selected the Hi Z setting on your interface if it has one. There is an input testing feature in TH2 that helps you get your input level set properly so look check that out. Also click the Master button at the top of the TH2 GUI. THose are the global controls that adjust overall levels and that's where you'll find the Gate which is crucial for keeping away unwanted noise.
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That post got eaten by the forum before you posted your reply.
Here is a step by step that SHOULD make it work:
1) Plug in the guitar to your interface. Choose the Hi Z (Instrument) setting for the input if it has one.
2) Insert a MONO track into your project.
3) In the mono track go to the Input dropdown and choose the input that the guitar is plugged into.
4) Make sure the tracks output is going to the Master or another bus that eventually leads to the master.
5) Click the track's Input Echo button so it is ON.
6) Turn up the input trim on your interface. You should now hear the dry signal of your guitar.
7) Insert TH2 into the FX bin. Make sure the little blue power button next to the effect is turned on as well as making sure the FX bin isn't being bypassed.
8) Select a TH2 program bank and open the Master section to make sure the volume isn't turned down or anything.
At that point you should be in business. If not something is wrong. Sorry to state the more obvious steps but I wanted to be thorough.
Cheers.