@DeeJoe.
Welcome to BroadbandForum.in.
Please mention the model No of your wireless
router.
step 1 Connect/Test desktop /
laptop to ethernet port with RJ45 from modem.
Step2 : Remove Rj45 from desktop and connect to WAN port of Wi-Fi router.
Step3 : run the installation wizard.
Step4 : connect another Rj45 from LAN1 to desktop. TEST
Step 5 Test laptop in wireless mode
If any problem report details. of 6 & 7.
step 6 : start/ run type cmd type ipconfig/all.
Step7 :Also check the diagnostics page of modem and router.
Reference :.
DI-524
select you model from bottom of page ( left hand side menu)