Question Pc won't post after changing bios settings

[Blastoise2]

I have a Gigabyte P35-DS3R which I used in a build a few years back as a project pc and back up. Pc was working fine and installed operating system with no issues. But now a few years later I want to upgrade to a ssd. So I wanted to change in the bios settings so that the dvd drive will boot first from the windows 7 disc, but after changing the boot order, or in fact any setting and then save and exit, the computer begins its shut down process but seems to power down too early or a few seconds earlier than what I would expect. Then I start pc again and it won't post. So I have to remove the cmos battery and then it starts up and posts.

What could be the the issue?

I also tried holding down f12 to choose where to boot from but the keyboard doesn't respond, I tried to enable keyboard input in bios, but the after save and exit it won't post, and have to remove cmos battery and start again

Am I stuck with using my mechanical hdd?

 

[RARRAF]

well just maybe the bios battery is out of date buy a new one and try only 3-4 pounds

 

[Blastoise2]

well just maybe the bios battery is out of date buy a new one and try only 3-4 pounds

But it works when I'm using my mechanical hdd when I shut down and turn computer on the next day. The time is saved. Its o ly when saving the bios and exiting that it doesn't post. I'm not sure if replacing the battery would help. But I can possibly buy one in a few days.