Well it's not a mystery I don't think. If the original injury was bad enough and you just took time off then prob it basically just "healed wrong." Scar tissue and the loss of flexibility/pliability and, if it were the muscle, contractile properties is the problem.
Definitely a physiotherapist is a good idea especially for a chronic problem cuz they have tools that can really help in remodeling the tissue and will be better equipped to evaluate you particular injury to plan a suitable rehab.
The first post in the Injuries sticky, as Sentinel mentioned, will tell you the basics of what to do. Mostly ignore the first aid stuff, i.e. R.I.C.E. since it's too late now!
I will give you the basics of what you need to do stressing that I am not a doctor, blah, blah, blah. If you pay attention to your body and do it STEP BY STEP, though, I don't think you will further damage yourself. You have to take it slowly and methodically if you ever want your biceps to work right again and not continually get reinjurred.
Unless you think you have a active injury (look up acute vs. chronic muscle/tendon injuries and symptoms) then there is not use of taking complete rest again. You will need to take time off from lifting and begin ACTIVE recovery.
The one thing to keep in mind is that all this is depending on whether this is in fact an old injury or whether you have reinjurred it. That is for you (and a doctor?) to asses. Scar tissue is easy to tear and that can result in more tearing of surrounding tissues and and even worse injury than before. So IF it is active then start from the beginning and use R.I.C.E. therapy then go from there.
Here are the basic tools if it is rehab of an old injury but the injuries thread will give you more details.
HEAT (NO HEAT for NEW INJURIES...ICE ONLY)
STRETCHING
MASSAGE
No weights for the first 2 weeks up to perhaps 4 weeks. The goal here is to begin remodeling the tissue and regain normal flexibitity and range of motion. NO PAIN. If it hurts at this stage don't do it. Only slight discomfort is allowed.
There are different types of stretching you can use. I would recommend trying PNF stretching at the end of this phase. It combines stetching with isometrics and I think it will work wonders and be much better than just going from the stretch/massage phase into isometric exercise. It should get you ready for some very light weight high rep work.
Everything hinges on how it feels so you'll have to evalute your progress but I wouldn't do anything else but heat-stretch-massage for at least two weeks. Then you can try out light weights. Do what is comfortable. If just holding a weight hurts then you can't hold a weight. If you can't lift a weight then you may still be able to do some isometrics (and PNF). When you do hit the weights it will have to be pretty high reps.
HST may be a good choice for a program in this rehab. Starts with high reps and supmaximal weights so it shoud be perfect for slowy building back up work capacity but ONLY after there is no pain and flexibility is regained (flexibility and pain will go hand in hand here).
Hope some of this helps
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