i can't connect my epson printer to my laptop by wifi.

What type of wireless, Bluetooth? If so, you need to peer it with your Windows 7 PC.

Click Start > Devices and Printers

Click Add Printer on the command bar

you may try the Printer troubleshooter, which will attempt to automatically diagnose and fix your problem.

Open the Printer troubleshooter by clicking the Start button  , and then clicking Control Panel. In the search box, type troubleshooter, and then click Troubleshooting. Under Hardware and Sound, click Use a printer.

If Windows can't detect a printer that you want to use, follow these steps to find and add the printer manually:

1. Open Devices and Printers by clicking the Start button  , and then, on the Start menu, clicking Devices and Printers.
2. Click Add a printer.
3. In the Add Printer wizard, select Add a network, wireless or Bluetooth printer.
4. On the Searching for available printers page, click The printer that I want isn't listed.
5. On the Find a printer by name or TCP/IP address page, choose how to find the printer that you want to use, based on the type or location of the printer, and then click Next.
6. Complete the additional steps in the wizard, and then click Finish.

To make sure that printers on the network are being displayed, check to see if the network is working correctly. For more information, see View the status of your network.

I’d also suggest you to refer the link below and follow the steps mentioned in the article to troubleshoot network printer problems:

Troubleshoot network printer problems

http://windows.microsoft.com/en-us/windows-vista/Troubleshoot-network-printer-problems

The above article is for Windows Vista. It applies to Windows 7, too.