The two buttons on the front at the top are:
1st button = WPS (Wi-Fi Protected Setup) to automatically connect to a wireless device which also has WPS feature. Avoids necessity to enter the wireless key on that device.
2nd button = Toggle on/off the wireless function of the router. If you toggle it off, it's green light goes out, as does the green WPS light above it.
It's explained in the setup manual:
http://www.downloads.netgear.com/files/GDC/DGN2200V4/DGN2200v4_NA_IG_6pcvr+interior_14Mar13.pdf
For slow internet speed or dropped connections on Wi-Fi, open the router's configuration utility (also explained in the setup manual - page 9) and try changing the wireless channel to a fixed channel number instead of the default "Auto" setting.
Choose a number between 8 & 12, then click on the green "Apply" button at the top.
Don't change any wireless settings with a wireless-connected computer, use a wired connection instead.