Have 2 different memory's one being {CL2} & {CL3} the other ,will the two memory's work TOGETHER or maybe CAUSE trouble or maham??SET the memory speed to the slower one, CL31.  They'll work if they are each within the range of memory module parameters your motherboard chipset will support.  Your system will attempt to RUN with the lowest common denominator set of memory module parameters.

2.  Serial Presence Detect (SPD).  When you boot, motherboard BIOSes read the SPD information from your memory module(s) to configure the memory controller.  Either your BIOS automatically selects a common parameter set acceptable to your memory modules or you set them manually within the BIOS.

3.  Test the system memory.  You can do this by booting a standalone memory diagnostic program from either floppy or CD-ROM DRIVE.  See MemTest86.  Follow the "Free Download" link to either the floppy:
    Download - Pre-Compiled Memtest86 v3.4a installable from Windows and DOS

or CD versions:
    Download - Memtest86 v3.4a ISO image (zip)

If it passes the memory test without errors (run several complete passes or overnight), there's not much else you can test; you're good to go.