My PIR sensor always shows HIGH output even when no motion is there

My PIR sensor always shows HIGH output even when no motion is there. I've benn trying for last few days still it isn't working. Before 2 weeks, it was working alright. But now, what has happened it always gives HIGH output. What can I do to fix this problem?

the code is
int led=4;
int pir=7;
int buz=2;
void setup(){
pinMode (led, OUTPUT);
pinMode (buz, OUTPUT);
pinMode (pir, INPUT);
}
void loop(){
int value= digitalRead(pir);
if (value == HIGH) {
digitalWrite(led, HIGH);
digitalWrite(buz, HIGH);
}
else{
digitalWrite(led, LOW);
digitalWrite(buz, LOW);
}
}

Please help me. I have to submit my project in school after 9 days. Anyone please help me :sob: :sob: :sob: :sob: :sob: