Open computer and reseat memory
Sometimes when the computer is moved or over time a memory stick can become loose causing the computer to be unable to read the memory or get errors as it's reading it. Try fixing this issue by opening the computer removing each of the memory sticks you have in the computer and then placing them back into the computer.
Swap memory location
If reseating the memory did not resolve the issue try swapping the location of the memory. If you have only one stick of memory in the computer try moving it to another slot and then boot the computer.
If you have more than one stick of memory try removing all but one stick of memory and boot the computer. If this does not resolve the issue try removing that stick of memory and try one of the other sticks of memory.
Try another computers memory
If you have access to another computer that uses the same memory, try using its known good memory in your computer.
If another computers memory works you know that you have bad memory. If another computers memory does not work and it is compatible with your computer unfortunately your motherboard or the slots on the motherboard are defective causing it to be unable to properly read the memory, which means the motherboard will have to be replaced.