Maybe it's lockup in the following loop and is that the reason that it is not responding..?
while (client.connected()) {
if (client.available()) {
if(!sentHeader){
// send a standard http response header
client.println("HTTP/1.1 200 OK");
client.println("Content-Type: text/html");
client.println();
sentHeader = true;
}
char c = client.read();
if(reading && c == ' ') reading = false;
if(c == '?') reading = true; //found the ?, begin reading the info
if(reading){
readstring += c;
}
if (c == '\n' && currentLineIsBlank) break;
if (c == '\n') {
currentLineIsBlank = true;
}else if (c != '\r') {
currentLineIsBlank = false;
}
}
}