If you are absolutely sure that your UST and voicebank are of the same type, then these are the only things I could think of at the moment:
What language is your UST in? If you UST uses romaji and your voicebank can only read Hiragana, or vica versa, your Utau won't be able to read it and therefore won't make any sound. To check what language your voicebank can read, you can go into their voice files. If your voicebank's wav files are titled with symbols like "あ", or "か", that is hiragana. If the tiles are more like "a" or "ka", that is romaji. If your UST and Voicebank's symbols do not match, you can try to download a plugin that can convert romaji to hiragana, which will help change the notes to something your voicebank can read. Adding plugins to Utau is just like adding voicebanks, you just put them into the plugins folder instead of the voice folder.
Does your ust have any extra symbols after the lyrics, such as 囁 or _弱? (some have underscores, some do not). These are called appends, and are extra voicebanks that some Utauloids have recorded,. However, some will not have these banks and therefore cannot understand these symbols. If this is the case, click ctrl+a, then at the top of your screen click Tools, then Built in tools, then Suffix Broker. Leave the suffix broker blank, then click OK. This will clear any appends.
If this is not the case, maybe you could try fitting the UST to your voicebank? First, hit Ctrl+A to select all of you notes, right click on a note, and then hit Property. Once you see the menu pop up, make sure that STP is empty. Then, to the top right of your screen to the right of the MIDI buttons, you will see a variety of different options. Click these buttons in this order: Reset, P2P3. It might also help to hit ACPT which will reset the envelopes. That should help fit your voicebank.
You might have to do multiple of these things to get it to work.