Which model of HP Pavilion has 3 RAM slots?
Download CPU-Z [ http://www.cpuid.com/cpuz.php ], go to the mainboard tab to see the manufacturer of the motherboard. It may or may not show the exact model number, but that is ok, since the important thing is RAM information. Go to the SPD tab, it will show the currently installed RAM speed and type. Check the type of the originally installed RAM module. Manufacturer of the RAM doesn’t really matter, you only have to worry about the type (i.e. DDR1 , DDR2) and speed (i.e. PC-2700[333Mhz], PC-3200[400MHz], PC2-4200[533MHz],PC2-5300[667MHz] etc.). If you have RAM modules with different speeds, then all will run at the speed of the slowest module. Usually when RAM is incompatible either the computer won’t boot or the incompatible RAM module will not be detected at all. If you experience random system crashes, that seems to me like a faulty RAM stick (most probably not a compatibility issue). You can use a tool like memtest86 [