First, it's difficult to answer without knowing the exact brand and model of your wireless router. Even then I'd just have to go to the manufacturer's web site to look up the installation guide - which you should do.
Also you say the router is locked. To get to it's login and settings you have to go to it's IP address, using your browser. Put the IP address where you usually put web addresses (without the "www")
That is, do so after your internet modem is connected to the router with an ethernet cable to the "WAN" port and your computer is connect by an ethernet cable to one of the router's other (usually 4 ports) - all with the power off. Then turn on only the router and wait (like 1 minute) for all the lites to settle down (it has to boot up, kind of like a computer). Then turn on the computer.
The problem is you have to know the IP address (your router's address on the local network - all network devices have a unique address). Local IPs always start as "192.168.x.x", but it's hard to guess those 2 missing"x"s. Use the advice from others above to try to determine the actual IP address. See if the label on the router might tell you the IP address.
Here's what you could also do:
1. Determine the brand and model number of your wireless router.
2. Go to the website of the manufacturer and look for a "Support" or "Installation" link or such. They will have step-by-step instructions and possibly a video.
3. Try to use your new computer attached directly to your Internet modem first (no router), just to get online to the manufacturer's site. Then connect up the router and follow the instructions to set it up later.
If you can't use your own computer, use a friend's or a public computer at a school or public library and write down the instructions or print them out.
4. Your router should have a red "Reset" button somewhere (or maybe a little hole you insert an unbent paper clip into for a reset button). If you can't do anything else, you can use that reset button to return the router to the state it was in when first purchased. Then the IP address, user name and password will be exactly as in the manufacturer's setup instructions. You'll have to redo all necessary settings, but that shouldn't be hard with the manufacturer's instructions.
Hope this helps....
_jim coe