What you did with the settings (or removed battery, dvd player etc), as you mentioned it was initially showing all the channels.
- actually FM Radio bandwidth in Japan is somewhere aroung 76MHz - 90MHz, and our Pakistani FM range is as per European/American standard 88MHz - 108MHz.
So, japanese radios can only play 2-3 channels which are falling in the range of their radios.
there are two options to rectify this:
1- Either find some settings if your radio has an option to select between two frequency ranges (i havent seen any japanese radio having this option, but as you said it was previously showing all channels, so your radio might have this option as it is some newer model)
2- second option is to install a FM Frequency converter before the antenna cable, so it will convert the frequencies according to this radio. for example, Screen will show you 76MHz but it is playing channel of some frequency like 91 MHz.
cheap (low quality) frequency converters are available for Rs. 100-200/- at almost every car audio shop. But if you want a high quuality, you have to search it.