If when you say you "placed it in the headboard of your bed", you mean one of those storage headboards and the fabric was in contact with the wood for all that time, it is the acid in the wood that caused the yellowing. That's why all the warnings about acid-free storage, etc. Try any of the following to brighten it back up (as was mentioned, you have not much to lose).
a vinegar rinse - one part white vinegar with four parts warm water.
soak in false teeth cleaner and water mixed according to package directions - rinse several times (best to test a small piece first with this method).
soak overnight in a solution of non-chlorine bleach (1/2 cup dry oxygen bleach mixed in 2 gallons water). - use a plastic, glass, or stainless steel tub - remove any obvious stains with a stain removing laundry spray - then wash in hot soapy water and rinse in warm water - use distilled water for the final rinse in any of these methods
if it is just mild overall yellowing, you can use bluing, it's still sold in grocery stores
Good luck.