I'm going to go ahead and suggest a power cycle/CMOS clear even though I know I'll probably get yelled at because the problem "has nothing to with the CMOS, you're a loving idiot."
Nothing to lose, could fix the issue. Doubtful, though. He said that the problem is occurring in the Windows boot-screen, which means it's clearing both POST and BIOS just fine.
I want to keep this option for later I want to know if there is anything else that I can do first, any options in the BIOS for example?
Aside from the CMOS clearing as listed above...no, not particularly. I understand it's a pain to keep switching the cards, but we need to determine quickly where the problem lies. It's very possibly that you're not correctly installing the card (such as not supplying it the right amount of power or putting it in the wrong PCIe slot).
The BIOS lets us toggle basic configuration settings, but there's honestly not much settings relating to AGP/PCI/PCIe cards, and not much that would outright cause a crash. Besides, if anything is wrong with the BIOS, it'd be more likely that your BIOS isn't updated to support UEFI (required by the GTX 750Ti if what I'm reading is correct), at which point we'd need to be able to log in to the computer to update it.