Verify that the power adapter is 5volts, 1amp. You may want to try replacing the micro-USB power cable as well.
Sounds like the power plug may have failed. Try replacing it.
Little confused how your Internet being down is being caused by the Roku? Or do you just mean Internet TV?
As noted, most Roku's use standard USB charger-style power supplies. You can always try any charger you have, as long as it's rated 5V 1A OR MORE as @AvsGunnar noted. If you have one of the stick models, you must use the Roku cord as that is also the WiFi antenna. Otherwise, you can even use another USB cable, although that is unlikely to cause low power problems.