i bought i new plantronics rig headset and the my laptop had 3 jacks one for headset and one for mic and i got a PC splitter plug them in and my msi laptop is still not recognising my microphone that is in my headset
If it is a single jack headset, but you split it to connect to two ports, then it is likely either the port is the problem, the splitter is, or the headset mic isn't working.
I would test the headset on another device to make sure that it isn't the problem. Make sure this is a device that does not need the splitter. If it works fine, then you are down to the splitter or the port being the issue. Or perhaps the system.
While it is connected to the computer (through the splitter) try the following...
Go to "Control Panel".
Click on "Sound".
Click the "Recording" tab.
Click on the device you are trying to fix.
Now click the "Configure" button and then click "Set up Microphone".
Once that is complete, click the "Properties" button.
When you are done with your changes, in "Properties", click "Apply" and then "OK".
Then click "OK", again, on the main "Sound window".
If this doesn't resolve it, try connecting the headset just to the mic input. Yes I know that isn't what you need, as you need the headset also, however this will allow you to see if the splitter is the problem. If the mic works when connected directly to the mic port, then the splitter is the issue. If it still doesn't work when connected directly, and the above steps don't fix it, then the port is the issue.
A way around that is to get a 3.5mm to USB adapter and connect through that, or have the mic port replaced.