I don't know how old this computer is, but first I would recommend you update your bios to the latest version.
Next try this: If the computer is a desktop, unplug it from power, then after a few minutes plug it back in. If the computer is a laptop, remove the battery first. Does that work?
Another idea: Most computers have a BIOS setting that says something like quick POST (Power On Self Test) or FULL POST. Select FULL post, this may redetect your ram on every boot.
Note: Even if these things work for you, you should run a program like memtest86 to verify that your memory is indeed working to spec when it does show up.
I know you likely don't want to hear this but, your computer is likely not compatible with that RAM if you are having this problem in the first place, that shouldn't happen normally under any circumstances. Your motherboard perhaps is defective or perhaps it is a junky cheap model, or perhaps you got no name brand RAM, who is the manufacturer?
Clearly things are not intended to work that way. It sounds like it is likely the motherboard or BIOS's fault, but stop doing that, you will wear out the slots and have to buy a new motherboard once it stops working altogether. Removing and re-inserting ram is not intended to work like plugging in a flash drive, you will likely break it (further) if you keep doing that.
These are some ideas given how little you wrote but you are not providing anywhere near enough details to properly diagnose your problem. You should at least write something about what kind of computer this is. I mean technical details, model, make, specs, etc not "it's a mac" or "it's a laptop".