I haven't used it in a couple of years, it's in excellant condition I think, but it has a code flashing and I am unsure what to do.

That's what I will try and do. Here's what we need to do:

Sony® camcorders nowadays have a built-in rechargeable battery for retaining time, date, and other settings. Since the built-in rechargeable battery is not removable, current camcorder models can only be returned to the original factory settings by pressing a small RESET button on the camcorder.
Older-model camcorders (prior to the year 2000) do not have a built-in rechargeable battery or RESET button, and require a manual power reset.
IMPORTANT: To determine whether or not your camcorder has a RESET button, or if model-specific information is required to complete any of the steps in this solution, refer to the operating instructions supplied with the product. Manuals are available online in the Manuals/Specs/Warranty section of the Sony® eSupport Web site.
Follow the appropriate procedure below for your camcorder.
Using a RESET button

1. Locate the RESET button on the camcorder.
2. Use a pointed object (like a ballpoint pen) to press and hold the RESET button for 2-3 seconds.
3. After 2-3 seconds has elapsed, release the RESET button.

1. Turn off the camcorder.
2. Disconnect AC power adapter.
3. Remove the battery pack.
4. Remove the lithium button-cell battery.
5. Move the POWER switch to the CAMERA position for 15 seconds.
6. Move the POWER switch to the OFF position.
7. Reinsert the lithium button-cell battery.
8. Reconnect the AC power adapter or reinsert the battery pack.
9. Turn on the camcorder.

Hi, this is a common problem with sony DCR-PC series camcorders. The cause is the loosening or loss of one of the rubber rollers inside the tape-deck mechanism. You can try tapping the top of your camcorder (where the flash shoe is located) and see if they problem goes away. Look inside your tape-deck and see if the rubber roller is still there, if you dont see a rubber roller, then the tapping may not work. Then your only solution will be to replace the rubber roller, which may be quite difficult as this part is hard to get since Sony no longer makes the DCR-PC line of camcorders. Another workaround is to use the tip of a can of compressed air (used to blow debris off keyboards, etc) you can buy at office supply stores. Strangely, the round plastic tip approximates the same size as the missing rubber roller, fits the metal spindle that holds the missing rubber roller perfectly and can be used as a replacement successfully to get rid of the dreaded C:31:23 message. Here's a thread that discusses this problem: http://wvstephens.blogspot.com/2008/05/sony-handycam-c3123-3123-error-easy-fix.html