E74 = AV cable error. Could be a faulty AV cable, scaler chip (usually caused by overheating), or less likely, GPU.
It would appear that Microsoft also offers their extended 3 year warranty for this error:
http://www.gizmodo.com.au/2009/04/mi...ror_victims-2/
Don't know if it will be your system repaired or a refurbished unit you get back (I would assume this policy differs between countries).
If it were me, I would try Best Buy first and see if they will honor their store warranty. If they don't then I guess you have to take the risk with Microsoft, pay someone else to fix your system, do it yourself if you are brave, or buy a new one.
At least it would appear that if it is less than 3 years old, it will be rectified for free.