Flashing green circle at start up

Change the DVD drive belt - both the original Xbox and RROD-prone Xbox 360 are known to have DVD belt problems. It’s common enough you really need to keep some on hand to fix it, or be prepared to order them. In order to change them, Refer to this guide to open the Xbox and change the belt/inspect the electronics. Power tools help with how long the screws are, but it’s not required.

NOTE: Sometimes you can “tap” the drive and get it to open, but that’s not a good fix. It works in a pinch, but you need to change the drive belt or lubricate it if this occurs, and it still reads discs.