I finished building my pc a few weeks ago but now it keeps freezing randomly (it did not do this right after the build), the screen freezes and you can not move the cursor but it does not crash or give a bluescreen. This is my first build so i might have done something wrong whilst building it. And i have noticed that my hard drive LED is always on (it worked before so its not wrongly connected).
Please provide the link to the memory that you bought (if you did it online).
I think your motherboard isn't setup properly for the RAM. You need to change the timings to 9-9-9-24 and 1.5V if it's DDR3 1333mhz.