Hello, I have a 2007 iMac AL (20" 2.4GHz, 6GB Ram, 2TB hard drive) running Yosemite (current on updates). I wiped the iMac clean late last summer (ca. July 2015) and rebuilt it with Yosemite (was on Snow Leopard). To my knowledge there are no apps on it that are heavy web users (apart from CrashPlan, which mainly runs between 2AM and 6AM). We have cable internet (Xspendity by Comcash) and a Netgear C3700 Cable Modem/WiFi Router (1 year old). For a couple of years we've noticed times where our internet just crawls or doesn't even work. The new router/modem didn't change things, really (but got rid of modem rent). Our network has an Apple TV, Macbook Air, Vizio Smart TV (ironic, I know), Ooma VoIP phone, and the iMac. Sometimes my 3-year old Dell work laptop. Everything but Ooma runs via WiFi. Connecting a laptop via Ethernet cable yields high speeds -- but not a practical option. Recently I shut the iMac down cold to test my theory. Sure enough, internet has worked great. When I start it back up, sometimes it crawls, sometimes it doesn't. I realize it has an older 802.11a/b/g/n card which slows everything on that SSID to the same speed -- but it shouldn't drop to dial-up level speeds (or stop altogether). 802.11n should be rather snappy. Any ideas what's going on with the iMac that could cause this? OTHER NOTES: * Same effect if online backup (CrashPlan) is enabled or disabled. * Only change noticed when iMac is on. Doesn't appear to be others using our network. * Even so, network password has been changed. No signs in router logs of others using our network. * Family of four. * The iMac is ~15' from the router and not connected to any other devices.