BIOS ROM checksum error + incompatible BIOS size on motherboard page (MSI 865GM2 v1.0)

[Lazyad07]

Hey all, I have an 865GM2 v1.0 which randomly went into a BIOS ROM checksum error after plugging in an IDE HDD after fully unplugging the motherboard's power. I have unplugged the drive, taken out the CMOS battery in an attempt to clear the error, yet I am met with the same screen. Additionally, the BIOS chip on this board is an SST 49L002A, which from what I've read can only hold up to a 256KB BIOS ROM. The official page for this motherboard only has 512KB BIOS ROMs which aren't any use to me unfortunately if I do need to end up flashing a new BIOS onto this board (unless there is a workaround I haven't heard of, in which I pray).

I have attached some images for reference, in which the one of the BIOS properly POSTing was before plugging in the hard disk.

Many thanks!