Replacing/Upgrading hard drive.

I have had trouble with my Cosmos III's drive being slow, so have been attempting to upgrade it. I bought a 850 evo to replace the hybrid drive it came with, as I knew that the 850 was one of the options and should be compatible, right? Instead I have had endless trouble with it, after having to find a workaround for cloning my drive and then finding that I cannot force my BIOS to recognise the drive, nor update the BIOS for compatibility. I am at a complete loss as what to do, and feel like I have wasted my money.

Note: The operating system recognised the new drive when I plugged it in externally, but when attached via SATA inside, it is invisible to the BIOS.

Anyway, if anyone else is having this problem or can help me I would be grateful to hear about it.

It certainly wont be the bios failing to recognise it, literally the only thing I can think is that its not plugged in properly/something has been damaged on the drive or the motherboard. if you install the old drive does it recognise this?

I eventually found a workaround where I replaced my optical drive with a caddy. Now working fine.