Can a PC run without SSD?



Match RAM sticks between matching slots (typically 1-3 and 2-4). Generally, you will not have stability issues even if they're different timings as the board will run them at the slowest timings, but you might.
 

There is no guarantee that it will work out-of-the-box, some manual tweaking may be necessary or it might not work at all. You won't know until you try.

In principle, it should work as that's what standards are for. In practice, mileage varies.