Some things you can try here, listed in the order you should try them.
Many times these measures will resolve a lot of intermittent issues.
- For wireless connections, remove all the stored wireless profiles and search for networks. You'll have to enter the encryption key again, which is sometimes the issue for connection problems.
- For wireless connections, change the channel on the router, I like channels 1, 6, and 11 in the US.
- For wireless connections, try moving either the wireless router/AP or the wireless computer. Even a couple of feet will sometimes make a big difference.
- Update the network drivers (wired and wireless) on your computer to the latest available.
- Update the firmware to the latest version available on the manufacturer's site.
- Reset the router to factory defaults and reconfigure.
Many times these measures will resolve a lot of intermittent issues.
