According to the data sheet (link in post#1), for reading, 'R' needs to be sent.
The posted code could never have worked properly.
If you type in an 'R' on the serial monitor it will be converted to lower case 'r' by the tolower() function, and that will never be equal to uppercase 'R'.
computerdata[0] = tolower(computerdata[0]); //we make sure the first char in the string is lower case.
if (computerdata[0] == 'c' || computerdata[0] == 'R')time_ = 600;
...
Wire.write(computerdata); //THIS WILL SEND 'r'
Get rid of the line containing the tolower() function, and carefully study the rest of the code to see if there are other glaring errors.