Re: please help
1) I am not familiar with the 89C2051, but I looked at the datasheet and this micro has no EEPROM, nor has it any way of self-programming the FLASH. That means that the IR code you enter is simply stored in RAM. So when you power down the circuit, the code is lost, which explains why it will not start after a powerdown. I am puzzled about why the brightness up and down still work after a power loss, but it may be just a weird coincidence.
In short, I think it is normal for the circuit to lose the code when powered down.
2) I suppose you are running at 220VAC. In that case each of your 47k resistors will dissipate about 0.25W. If they are rated for 0.25W each, then they may eventually fail, especially if there is a voltage spike on the line.
Replace them with at least 0.5W-rated resistors.