Hi birkdalite. A BIOS ROM checksum error means that the when BIOS tests the ROM for data integrity during POST, it has found an error. What the checksum is, is a figure that it stores, and it performs a mathematical process on all the ROM data, and compares the result with the checksum. If the two numbers agree, then the stored data hasn't been corrupted. If the numbers don't agree, then there is an error in the data. Unfortunately the only way of changing the data in the ROM is by flashing it. If your motherboard supports floppy disk BIOS booting, then you can flash the BIOS ROM even if the data has been corrupted. I notice that this facility is now included in ASUS motherboards. On other motherboards, a checksum error often means that the motherboard is scrap.
A BIOS ROM checksum error cannot be caused by a Windows error.