Running Memtest is a good starting point but if you have more than one stick of Ram you are better to do a physical test of each stick individually, see below;
How to physically test your Ram.The following checks require the computer case to be opened so take the following safety precautions 1st, disconnect the power cord from the wall socket and take anti static precautions before touching anything inside, you can do this by touching a bare metal part of the case.
Have a pencil and notepad to hand.
Remove each stick of Ram and blow out the memory slots.
Insert the first stick of Ram in memory slot one, reconnect the power and in the case of a desktop computer the video to screen cable.
Power up the computer and see how it goes.
Make a note of the results.
Repeat the procedure until the first stick of Ram has been tested in each memory slot and the results written down.
Remove the first stick of Ram and put it to one side on top of a piece of paper with the number one on it for identification purposes.
Repeat the procedure with all Ram until each stick has been tested in all slots, the results written down and the sticks identified numerically.
Please note that some MBs (motherboards) will not boot unless there is Ram in slot one so please provide us with your motherboard details, brand, model name/number and any revision number, these details may be found by the CPU, between the PCI slots and/or around the edge of the motherboard, once we have the MB details we can look for the user manual.
To run the HDDs diagnostics tool;
Make sure you select the tool that is appropriate for the brand of your hard drive http://www.tacktech....ay.cfm?ttid=287
Depending on the program it'll create a bootable floppy or a bootable DVD/CD.
If the downloaded file is the .iso type use ImgBurn: http://www.imgburn.com/
to burn the .iso file to a DVD/CD disk depending on your OS (select "Write image file to disc" option) and make the disk bootable.RE ImgBurn: please use the custom install and uncheck the attached foistware such as "Install Entrusted Toolbar etc
If you are using an add on video card tell us the brand and model name or number of the card and the same for the PSU.