There are a lot of reasons why your computer’s memory becomes unstable or does not operate at all. The simplest reason is the usage of memory modules of unauthorized producers on branded motherboards. A lot of companies that produce chipsets and motherboards, for example Intel, try to fight with this piracy. The best way to achieve stability in memory operation (especially if your computer is still under warranty) is to change the bad memory module in a shop. It often happens that two modules from one batch differ much: while one module operates well, another one does not operate at all.
Memory failure is a very wide-spread problem during the processor overclocking. A processor overclocks but there is a message about memory failure during self-testing. There are two ways for solving this problem. The first one is to return to the current values of BIOS settings or the hardware status if it was changed. The second way is to try to stabilize the memory operation, for example, by increasing or decreasing the supplied voltage. Even a small change in standard voltage (within 10%) may return memory to its normal functioning.