There are different ways to assign a static IP address to your computer, printer, NAS, IP camera or other network device and reasons why you'd want to. A common example is that you're adding a NAS drive to your home network, but in order to access it from the internet it needs to always have the same IP address.
If you don't assign a static IP address, it will be dynamically given an IP address by your router each time you turn it on.
However, unless you know what you're doing, you might cause a conflict if the same address is already assigned to another device on the network.
The correct way to assign a static IP address is to tell your router to always give the same IP address to a computer or other network device with a certain MAC address. This is a unique code - a bit like a car's registration number - which every networking device has.
First, log in to your router. If you don't know its IP address, open a Command Prompt (search for cmd in Windows 7 or 8) and type 'ipconfig /all' without the quotes and press Enter.
Your router's IP address is the same as Default Gateway. You can also see the MAC address for each network adapter (it's called the Physical Address) but make sure you note down the address for the right adapter (if there are several - laptops will usually have two, one for Wi-Fi and one for Ethernet) by looking at its description.
Type this IP address into a web browser’s address bar, preceded by http:// and log in with the username and password you set, or look in the manual or on the router itself for the defaults.
The Thompson DG585 router has a menu called Home Network, but it may be called LAN or Network or something else such as Bind IP to MAC in your router. BT's Home Hub helpfully has a 'Static IP' menu.
When you find the right page, you might see a list of connected computers, or you might have to select your computer from a list, or enter its IP or MAC address manually.
However your router handles it, enter an IP address in the same format as your router's: the same first three numbers, e.g. 192.168.1 and then a fourth number between 2 and 254, ensuring it isn’t the same as your router's address. Ideally, check the range of IP addresses which is used by your router's DHCP server, and pick a number outside of this range.
If you’re still having problems, you may need to refer to the documentation that came with your router. Alternatively, try visiting your router manufacturer’s website, or contacting their support department. Forums, such as PC Advisor's very own forum, can be helpful as well.