Monitor audio not working

Hi, I have a Dell Inspiron 5400 AIO but the screen has cracked. I have plans to fix it (I know the price is £400 - £500 maybe more) but until I do, I have been using a Dell E2424HS monitor with built-in speakers to connect to it. But ever since I bought it, the built in speakers have not worked. Can someone provide me with a solution?