Still I don't understand why am getting such voltage & it's the same feel that I touched 250 voltage of current. Also when I put two fingers on opposite direction (when I am removing polythene cover from the plastic board) I see a running current (blue colour) from one finger to other finger and it lights the whole place for a second & anyone see it clearly even in the day time. It hurts so much to me and starts pain in joints & muscles. I don't feel my body is releasing such power but, I feel I touched a large source of power. Do you have any Idea about this...?
The polythene/polyethylene covering, plastic board, and possibly your skin are creating significant static electricity via triboelectrification. Dry skin on human hands is near the top of the positive end of the triboelectric series while most plastics and plastic films are at the other opposite (negative) end. Simply sliding your hand across most plastics can generate significant surface charging of the plastic. In addition, if the plastic sheet is resting against a conductive (metal) surface, its possible that you, the plastic sheet, and metal surface create a high voltage capacitor that is being electrostatically charged tens, or even hundreds of thousands, of volts.
Small static discharges from your fingers to the charged plastic surface or polythene are faint and hard to see but easily heard as a series of small snapping sounds. The small sparks might sting a little, but they're basically harmless. However, if you can see a spark discharge from you fingers in the daytime, its likely that your body is part of a higher-energy capacitor discharge. Capacitor discharge sparks are bright blue or blue-white, they make a loud snap or bang, and they can be quite painful. Larger energy discharges can be dangerous or even fatal if they induce ventricular fibrillation in your heart.
Blowing air from a static neutralizer (air ionizer) may help to neutralize surface charges. Trying not to slide your hands across the materials to reduce charge buildup, changing the geometry of the "capacitor", or providing alternative discharge pathways (instead of through you!) are all possibilities. However, it's difficult to be more specific without knowing a bit more about your setup and the materials involved.