prefurbished RROD xbox from ebay

So the other day i bought a what a thought was a broken xbox 360 from ebay for a really low price, when i got it i cracked it open with the kit i got from ifixit.com and what i discovered was that the original user or someone before him had previously refurbished it, replacing the xclamps the thermal paste and pretty much everything. I continued to re replace everything in it, this was my first time doing it but i had no problems at all. When i put it back together to turn it on i still got the same flashing ring. assuming i did everything right any ideas on how to fix this mess?