Dell won't be providing Win 10 drivers for the Inspiron 620. System is too old...
If you open Device Manager, is the WiFi network card entry marked with a ! or X?
After you upgraded to Win 10, did you run the network connection wizard on the 620 to identity your WiFi network and did you enter the (WPA2) network password on the 620 to allow it to connect to the router?
Have you rebooted the router (and modem)?
Do you have the Dell (Atheros) 1502 WiFi card? If none of the above helps, you might try installing this Win 10 driver for the 1502 card. Be sure to manually set a System Restore point first, to be safe. Keep in mind this driver is for an Alienware system and I have no idea if it will work with an Inspiron.
Worse/worse, remove the existing WiFi card and replace it with an inexpensive WiFi card or plug in a USB>WiFi dongle that's compatible with Win 10...
Forum Member since 2004
I am not a Dell employee