Having an issue getting a new GPU to work

Hello, having a bit of an issue.

Earlier this week, I ordered a new GPU from nvidia, and I am having an issue with my PC booting up with it. I have it plugged in to the PCI slot correctly and it is receiving sufficient power, etc. The problem arises from my PC having secure boot enabled which is preventing the GPU from working. Now, I know that normally this could be fixed by disabling secure boot in the BIOS settings (Windows 7 updated to Windows 8.1, so I have BIOS and not UEFI), but I am unable to disable secure boot in my BIOS settings. There simply isn't an option for it, so I went to check my msinfo32 to see what version of BIOS I was running and if possibly there was an issue with that version. However, while finding that my BIOS was outdated inside of the system information, I also found that my Secure Boot State is listed as simply unsupported, not disabled or enabled. Thinking this was possibly just an issue with the version, I updated to the most recent available, yet the problem persists.

Any idea how I could fix this, or am I going to need to simply buy a new motherboard?