http://superuser.com/questions/952537/windows-10-wifi-cannot-connect-intel-pro-3945abg-wireless-card Windows 10 wifi cannot connect - Intel pro 3945abg wireless card - Super User
I had a similar problem, on two different Windows 8 laptops (one Dell Inspiron 15, one ASUS) recently upgraded to Windows 10. I thought it was the drivers, and maybe they have something to do with it, but my workaround is really simple: change the WPA key to be all-numeric. That fixed the problem
This solution worked for me, I thought I'd pass it on since many people will be upgrading to win 10 at the end of this month.
Thank you for sharing this with the community, we are glad that this worked for you.
For other users, please keep in mind that the Intel® PRO/Wireless 3945ABG Network Connection is not supported by Microsoft Windows* 10. This adapter has reached End of Interactive Support, and Intel does not have new driver releases for it.
This workaround may or may not work in your system, and trying this or other workaround in this configuration will be at your own responsibility.
http://www.intel.com/support/wireless/wlan/sb/CS-035711.htm Intel® Wi-Fi Products — Which Intel® Wireless Adapters Work With Windows® 10?
http://www.intel.com/support/wireless/wlan/sb/CS-035684.htm Intel® Wi-Fi Products — Which Intel Wireless Products Support Windows® 10?
Spoke too soon, if the system is left off for extended periods the wifi adapter becomes inactive, only a reset through the "diagnose/fix" dialog by right clicking the wifi system tray icon brings it back.
Still works, but with this additional annoyance.
Will attempt this work around
I have an older Lenovo laptop (XP, upgradeable to Vista) subsequently upgraded to W7 and W10, with the 3945ABG wireless adapter. By shutting off the power management feature through the Device Manager, it solved the problem with having to "diagnose/fix" the adapter.