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Toilet water tank? Potential flushing issue?

I opened the lid for my toilet suite, and cannot put it back. I cannot completely take our either. Was trying to flush the toilet then i noticed water is slowly filling up the bowl but didnt really seem to have enough power to flush. Then i thought i want to check inside the water tank. Lid was tightly attached and i opened it but it wasnt seperating completely but stuck with flushing button.. Cant really explain further. Can some one please put back the lid and the flush botton. (Potential replacement of parts inside?) And check if flushing is ok (potential blockage?)