Preliminary checks
You should first check the model of RAM stick that you have on the manufacturers site for the recommended voltage setting and then make sure it is set correctly in the PC's Bios. An incorrect voltage setting may be the reason for your problems so test the PC's performance again if the voltage was incorrect.
Errors can also be caused by dirty contacts, mismatched sticks or using them in the wrong slots. Check all sticks are the same make and specification, check the motherboard manual for the correct slots to use. Remove all the sticks and clean the contacts with a soft pencil eraser and blow out the slots with a can of compressed air.
Testing
Download Memtest86+ from here.
You need to scroll down the page until you see the three blue screenshots. Just below is the list of downloads for Memtest86+ V4.20. Click on Download - Pre-Compiled Bootable ISO (.zip) and save to your desktop.
When the download is complete right click the file and select Extract Here and burn the image to a CD.
In windows 7 right click the extracted file, select
Open With, then select
Windows Disc Image Burning Tool then follow the prompts. For all other versions of windows (if you do not have an ISO burner) download this free software.
isoimageburner
Boot the PC into the Bios setup and set the CD/DVD drive to 1st in the boot sequence. Insert the disk in the drive then reboot and the disc will load into dos. Leave the test to run through at least 8 cycles or until it is showing some errors. If errors show in the test, remove all but one of your RAM sticks and repeat the test on each stick until you find the one that is faulty. This is a long slow test and should ideally be run overnight.
The memtest will not be 100% accurate but should easily detect any major faults.
If errors show immediately then remove all but one of your memory sticks from the PC and run the test on one stick at a time to isolate the faulty stick.
IMPORTANT
Always disconnect your PC from the mains supply when removing Ram sticks and earth your hands to discharge any static electricity to avoid damage to sensitive components. If performing this test on a laptop PC you should also remove the battery before removing or replacing the RAM sticks.
