"this is always happen when I power the circuit or switch it off an on agian (but Not all the time some times it works somthly)."

I have not worked with the AT89C2051 but it sounds to me like you need to rework the way you are handling the RST line on power up. Possibly holding RST high long enough while power stabilizes. This is best handled by a Reset Monitor/watchdog timer device.
If I were to buy this product from you it had better start every time I turned it on or we would be exchanging some very unpleasant E-mails!

Hal