Firstly yes, you do need security on. You have a choice between the older WEP or the newer more secure WPA. But Windows 7 64 bit does not like WPA.
As long as your email, and Internet access are all working, then the best thing to do is have a good look at the manual, You have a lot of devices attached, are they hard wired or wireless?
In my Draytek thread I have posted a query about WPA and Windows 7. Mine never drops out, has a DTS system, A Regza television attached by cable, and I use my iPad and laptop wirelessly.
One thing you could try is the UPNP setting. It's most likely disabled by default, but remember where it lives when you find it so you can disable it again if it doesn't help!
A lot of menus really should be left alone, if you want to play, you will also find a backup entry somewhere in the system. This will allow you to restore the router to exactly the same settings as before you made changes. Save it to your desktop for easy access.