Your Signature HUD will give you a replacement HUD when:

• you click new HUD... on your help menu (/1.help or HUD Menu > HELP... > new HUD...), or
• it automatically detects that SL has borked it.

With this replacement HUD, all you need to do is wear it, and transfer your gear over from your previous (borked) HUD.

This should fix whatever problem you were having.

If it doesn't, and it's not a bug (e.g, it's worked before) or it's not SL being SL, then you can try:

1. If the problem is a non-responsive gag or cuff (i.e. the gag or cuff doesn't respond - not the HUD), then just re-setup that gag or the one cuff (usually left-wrist or left-ankle, unless some other cuff is giving you problems). HUD Menu > HELP... > resetup....
   
2. If it still down't work, you might need to update your gear at the Update Switch.