Cant find Secure Boot in BIOS

I recently bought a new graphics card which I installed into my old Dell PC however it did not startup and beeped every twenty or so seconds. I did some researched and found my power supply was not enough for the new graphics card, so I bought a new power supply, which I also installed. It all works fine with the old graphics card but did the same beeping with the new graphics card. I did some more research and I believe I need to enable Legacy Support and disable Secure Boot in BIOS. After many efforts, I could not find either of these options in the BIOS and have no idea what to do next.

Also I'm not entirely sure on the model of the PC or anything as it is at least 9 years old and all I have is the stickers attached to the case (one of which says Vostro on it).

Any help is greatly appreciated.