Help! I have a HP Envy Photo 7155 printer that says it is connected to my WI-FI, but I can't set it up to my computer.?

Did you install the software that came with the printer? When you're running the installer, it should ask you how you want to connect the printer. Make sure you choose the wireless (or Wi-Fi) option. The program will then try to scan your network for the printer. Sometimes, it may not find it and you may need to find it's IP address. Exactly how you do it will be in the printer's manual.