Hello, I'll be happy to help you with this.
The most common reasons that a computer might not be able to connect to a wireless network are as follows:
- You have the incorrect wireless password, security key, or passphrase.
- Your wireless network is using a type of encryption not supported by your operating system, wireless adapter, or the wireless adapter's driver software.
- The MAC (hardware) address of your wireless adapter has not been authorized to work on your wireless network.
- Your wireless adapter is turned off or otherwise non-functional.
- You're having a signal strength or quality problem with your wireless adapter or router.
- Your wireless router is a multi-band capable router that is set to only use a band that your wireless card cannot use.
- As a less common item, I've occasionally seen the DHCP server on a wireless router set to only allow so many systems to connect to it, or only provide IP addresses to a specific list of MAC addresses (this is different from MAC address filtering and is generally called "address reservation"), and that that list of addresses doesn't contain the MAC address for your wireless adapter (which has a different MAC address from the wired network adapter).
As a first couple of steps, which will help eliminate quite a few other potential problems, I'd check to see if your laptop can connect to wireless networks in other locations (this will eliminate the possibility of the wireless adapter being turned off or being otherwise non-functional), perhaps at a coffee shop or library. After that, I'd check to see if any other wireless device is working with your router. If there are one or more wireless devices currently working correctly with your router, we can eliminate the possibility that the router isn't working at all. After that, I'd log into the router from a computer that is wired to it and manually verify the wireless network name (SSID), wireless channel being used, wireless band being used, encryption type, wireless password (or security key, or passphrase, or pre-shared key, depending on what your router calls it), and whether or not MAC address filtering is enabled (some routers call this an "access list" or something similar).
If you get that far and can confirm that you have the correct wireless network name, security information, and that MAC address filtering is either not enabled or the MAC address of your wireless adapter is entered in the list, and that your laptop can connect to other wireless networks and you have other wireless devices working on this wireless network, then the next step is to check with the manufacturer of the wireless adapter to verify that your security type is supported by the wireless adapter and its driver software. After that, check to ensure that there are non-reserved addresses still available in the router's DHCP server configuration.
If you would like clarification on any of these points, more depth in my answer, or if you have additional questions with regard to this matter, please don't hesitate to ask and I'll be happy to continue to lend a hand.