It may be the latches. Put your hand up and feel along the inside edge and see if you feel a lip or metal edge. This is the lever to release the latch. Normally there are two one on each end, move the lever out and this should release the shade. Also remove the buttons that the cords are attached to.
Now if you never repaired the shades, I would suggest taking it to an RV dealer and let them repair it. Now if your a gambler, it's not hard. After you have it down, find a large table to place it on. Now if it is a large shade you might have 4 strings, a small or medium will have 2 strings. Looking at the shade from left to right. The strings that come out of the left end go through the bottom edge and up the right side and across the top to a spring. visa versa for the right side. Take your time taking it apart and you can get it done. Good luck.
Renegade (Jim) & Wrangler (Doreen)
& 4 attack cats, TJ, Shadow, Chessie, RJ
along with 2 who adopted us, Tom & puddy.