why is it when i connect my laptop to my wi-fi it only connects for a second then says i have no internet access

Generally speaking, all connectivity problems fall into either of two categories:

Hardware or Authentication

The easiest way to determine where your problem lies is to find a free wi-fi spot (McD's or Starbucks, for example) and try to connect to their network.
The reason for this is because the networks are unsecured, meaning they don't require passwords and the encryption is typically WPA2 (default on all Wi-Fi routers/modems using 802.11 B standard or newer). An alternative would be to temporarily reset your router to its default settings (which changes the SSID, password, and encryption).

If you can't connect to any free Wi-Fi network, see if you can get your hands on a USB wireless adapter, and then try testing your connectivity using the USB adapter.

Note: that all wireless adapters are capable of detecting the available networks within broadcast range (if SSID is being broadcasted, that is), but if the encryption types/levels do not match, you won't connect, even if you have the correct password. That said, if your adapter doesn't support the encryption used by the network, you won't be able to connect.