You need to tell us the brand and model number of your components, including the RAM, the motherboard, the CPU heatsinkfan, the power supply and your graphics card at a minimum.
Download PC Wizard 2006 (free). Under the Hardware section, click on the Mainboard icon (green arrow pointing down to computer case), then double-click on "Chipset" in the list that appears in the upper right window. The bottom window will give a lot of info; print or write down the "Northbridge Information" and the "Memory Information".
Now, back in the upper right window, double-click on "Physical Memory", print or write down the info in the bottom window under the first "Information SPD EEPROM" section.
Also, download memtest86+ (self-booting, on either floppy or CD such as The Ultimate Boot CD) for later memory testing.