A method which sometimes works when a phone completely loses signal and network is to turn off the handset and remove the battery. By replacing the battery and turning it back on after a few seconds, you may find this solves the problem. This is because sometimes when a phone has been on for hours or days at a time it can cause a minor error. Turning off and back on often resets this error, and restores the phone to full working order.
If you have tried the above and are still not receiving any signal, then you should check with family and friends who use the same service provider. Have their signals dropped recently? Do their phones work in your house? If the answer to the second question is no, it would suggest there must be a problem with the local transmitter. The only solution here is to wait until the transmitter has been repaired before the signal will return to your phone.
However, if other people's phones are picking up a signal from your house, it could be worth taking your phone to a repair shop or to the store you originally bought it from. They will inspect the phone and hopefully locate the problem. If they can't help, it is perhaps worth contacting your network. Otherwise, unfortunately, it looks like you may have to purchase a new cell phone.