Many people today are suffering with the extremely frustrating red ring of death (RROD). The reason the RROD is so complicated is because the RROD can mean so many things. For instance, you could be dealing with a hard drive error, an overheating error, or a general hardware error.
Your error is most likely the E74 error, if it is, that is a good thing. You can get this error fixed for free at the Xbox support page, even if it is not under warranty. You can also check your warranty status at the support page. If you have an E45, E64, E65, E67, E68, E69, E71, E73, E76, or E79, you will probably have to pay $100 or more for the fix, if you want to send it in. I do not recommend this, you can buy repair kits online for cheaper.
Before ever sending in your Xbox 360, test it with different A/V cables, test it without the hard drive, and test it with a different power cord. Anyways, here is a general analysis of the errors for one red light.
E64, E65, E66-Disc Drive Error
E67, E68, E69-Hard Drive Error
E73-Unknown (Although it is possibly an Ethernet problem)
E74-A/V Cable Error, or General Hardware Error
E79-Hard Drive Error
There you have it, all the errors for one red light. Check the guide that came with your console because it has some general solutions to a few of the problems. You can use the Microsoft Support page to get you Xbox fixed. However, this can cost up to $100 and take over a month for the process to complete.