ReadFile problem(VC++)

[friendjin]

WriteFile(hCom1, "AT+CSQ\r", sizeof("AT+CSQ\r"), &dwWritten, &ovlw);
    Sleep(50);
                COMMTIMEOUTS comto;  
    comto.ReadIntervalTimeout = 10;  
      comto.ReadTotalTimeoutMultiplier = 5000;  
                comto.ReadTotalTimeoutConstant = 0; //dwTimeoutMs;  
                comto.ReadTotalTimeoutMultiplier = 0;  
      comto.WriteTotalTimeoutConstant = 5000;  
      comto.WriteTotalTimeoutMultiplier = 0;  
 
    f(!SetCommTimeouts(hCom1, &comto))
    {
    fprintf(Err, "%s\n", "Fail to get the response from the modem.");
    goto end;
    }
    int ReadError;
    ReadFile (hCom1, &szBuffer, sizeof(szBuffer), &dwRead, &ovlr);

This is part of code, the problem is while the modem is connectting, it is working all right.but while the modem is not connect well, or other problem form the modem, the programe will be stopped on the ReadFile().I mean the programe could not be stopped untill getting the response but actually no response in this case as modem error.I tried to set a timeout to exist while this error happens, but it would not work. I don't know what the problem is.
Any idea?
Thanks.