I had this happen to my old Inspiron. I researched online and concluded that it needed the motherboard reflowed. Not having any idea what that means, I'm just passing that bit of research along to you to try & help you resolve. Suggest you search Youtube for Dell reflow motherboard. It's something you apparently can do yourself, but I wasn't willing to try...   Good luck!

Seven beeps is either a mainboard or CPU failure - more likely the board than the CPU.

If you require further information, we'll need the model number and to know whether or not it's still under warranty.

Thank you