MemTest-86 is a simple but thorough tool which will scan your PC's RAM for errors. It's been around for almost 20 years, but is still being updated to fix bugs and ensure it works with the latest hardware (which includes both 32 and 64-bit systems, so don't be concerned about the "86").
The program comes in the form of an ISO image, so it's not quite as convenient to use as some of the competition. You'll need to use another program to burn MemTest-86 to disc (or create a bootable USB key) before it's ready for use. But once you have made those preparations, everything else works very well.
MemTest-86 boots immediately, for instance. There's no complicated operating system which needs to fire up, first - you're straight into the program's simple text-based interface. A menu offers a selection of test options, but you don't even have to worry about that: just wait a few seconds and the default test pattern will begin.
The screen then updates to show you exactly what's going on, the various tests that are being used. It's fairly technical, but if nothing else the "Pass %" and "Test %" will show you how far through the checks you are. And again, there are a lot of error types which could be reported at the end of the test (MemTest-86 is very thorough and detailed), but you don't really have to understand those, either. If you see any errors, there's a problem with your hardware; if you don't, your issues are probably somewhere else.
•Support for DDR4 RAM (and associated hardware), including retrieval and reporting of DDR4-specific SPD details. This includes DDR4 RAM that support Intel XMP 2.0 DDR4 RAM timings.
•New RAM benchmarking feature allowing results to be graphed and saved to disk. Previous results can be graphed on the same chart for comparison.
•New "Hammer Test" for detecting disturbance errors caused by charge leakage when repeatedly accessing addresses in the same memory bank but different rows in a short period of time.
•Added Haswell-E (DDR4) ECC support
•Added Xeon E5 v3 ECC support
•Added Ivy Bridge (non-Xeon) ECC support
•Added AMD Steppe Eagle ECC support
•Added Intel Atom E3800 SoC ECC support
•Increased maximum # of supported CPUs to 72
•Increased maximum # of supported RAM modules to 64
•Increased the number of supported memory controllers to 8