BIOS deleted Dell Vostro 1520

You could try removing the CMOS (coin cell) battery from the MB and see if that resets the BIOS but I highly doubt it would help. And to remove the battery you have to remove the entire motherboard from the system as detailed here. Unfortunately the MB is probably bricked and cannot be recovered short of sending the system to Dell if they would even work on it. Plus Dell would not recover the BIOS but in all likelihood would replace the MB. But on a system that is approaching 11 years old I would suggest you look into a new system.

turning off power in the middle of bios flash is a big no no.  If bios flash crashes, just let it restart.  Do not power off ever.

https://www.dell.com/support/article/en-us/sln300716/how-to-recover-the-bios-on-a-dell-computer-or-tablet?lang=en