There are several different causes for this issue - assuming the balance for other programs works as expected. The easiest to check and fix is the "Master Volume Control" You access this on a Windows PC by right clicking the Speaker Icon in the system tray (lower right corner of the screen). Select "Open Volume Control" Next,you'll see a box with Master Voume, Wave, CD, Wave, etc. These are the playback volume controls (shown below).
We need the Recording Control. Click "Options" --> "Properties" and select "Mixer Device". A drop down box should appear offering an choice of Input or Output devices. Choose Input. "Recording" should be selected in the "Adjust volume for" box. Place a check mark in each of the input presented. Mine looks like this:
Click OK to get to the Recording Control box below.
Here, make sure the BALANCE indicator is centered between the two speaker icons and the correct input has been selected - in this case, "Line Volume". Yours may be different. If already centered, go to the next step.
If the input levels are balanced, there may be a problem with the input cable. Try replacing the audio cables and try again. If your turntable uses a USB type connection that is molded to the turntable, you won't have this option.
If still no change, try connecting to another computer. If the problem is still present, it is in the turntable, somewhere between the last cable you can change and the stylus / cartridge. A stylus or "needle" can be replaced for under $10 or so (it's been a awhile since I priced these - so don't quote me) and simply plug into the cartridge. The cartridge is more expensive, but not too bad. Most cartridges simply plug in to a jack on the tone arm. Stylus and cartridge replacement is a do it yourself job and does not need to be done professionally - unless of course you want to have it done for you.
If none of these solutions work, there is some other problem inside the turntable. Most times, one of these steps will solve the problem. I hope this helps and good luck! Please rate my reply, thank you.