Convert Wired/Wireless Router to a Switch/Access Point

1. Connect your computer directly to the Modem/Router
2. Log onto your Modem/Router's web based configuration page
3. Navigate to the page that says "LAN" and then "DHCP Setup"
4. Make a note of "IP Pool Starting Address" and "Pool Size"
5. Disconnect the Modem/Router
6. Connect your computer directly to the Router/Wireless Router from a LAN port in the Router/Wireless Router. (Warning! Never connect to the WAN port)
7. Log onto your Router/Wireless Router's web based configuration page
8. Goto the page where it says "LAN"
9. Change the IP address to the one that you noted in Step #4, but outside the DHCP range. DHCP Range = ("IP Pool Starting Address") - ("IP Pool Starting Address" + "Pool Size")
10. Leave the entry of "Subnet Mask" as it is
11. Delete the entries under "Gateway" & " DNS Server". They don't matter now
12. Untick "DHCP Server". This turns off DHCP in the Router/Wireless Router, so now the Modem/Router will be the one acting solely as the DHCP server
13. Click Save
14. Connect the Modem/Router to a LAN port of the Router/Wireless Router
15. To make things working perfectly, you can do a repair of the "Local Area Connection" by right clicking the LAN icon in taskbar and select "Repair". If the "Local Area Connection" is missing from the taskbar, you can bring back it by right clicking "My Network Places" on Desktop and then selecting "Properties" OR by going to Start Menu → Settings → Control Panel → Network Connections. Then right click "Local Area Connection" and select "Properties". Then tick "Show icon in notification area when connected". You can also do a repair by right clicking "Local Area Connection" and selecting "Repair"

Done.