Why isn't my iPhone 5 being detected by itunes or charging?

Lately while I'm charging my phone, it would vibrate twice every few minutes. But today when I connected it it wouldn't charge. I tried connecting it to itunes but a box popped up saying " your device is not detected. Please unplug and try again." Please help!

Try another USB cable to see whether it's broken.

Most likely there's dirt in the connector or there might be a loose wire in the cable. Sometimes the wires break on the inside, such as if you accidentally rolled your chair over it after dropping the wire on the floor.
It happens.
So get some spare cables and try them. It's likely you will want to have them in the future anyway even if it turns out the one you have is not the problem.
You can also try plugging into a different USB port. So if you usually use the ones on the front, try the ones in the back, because those are usually connected to different pins on the inside of the computer, and so if it happens to be a problem with the computer hardware, then it's possible only one set will be bad.
Test some other USB device to confirm the USB port works.

Conclusion: it sounds like a hardware issue of some kind, but it is probably something you can fix, replace, or work around pretty easily.

Broken usb

Plug it into wall instead, it charges faster that way anyhow.