I have been using audacity for many trouble free years - currently - 2.0.5
I recorded one track tonight and when I hit record to record a second track audacity stopped responding. Now it wont launch at all. Using Windows 8.1 64 bit
Try WIN + X then Shut down (not the Power button and not shut down from the Charms Bar). This will perform a full shut down then you can start the computer again.
If you are using a USB recording device, try disconnecting it and reconnecting it before full shut down. Connect the USB device to an empty USB port, not to a USB hub that has other USB devices connected to it.
If you did not save the first track as an Audacity project then when you launch Audacity it should offer to recover your first track. If the track looks and sounds correct, export it as WAV. See Recovery - Audacity Manual .
File > New, drag in the WAV you exported then if all is OK you can close the recovered project without saving changes.
Look at Edit > Preferences… then Directories and make sure you have several GB of disk space in the drive you use for the Audacity temporary directory. Do not use network drives for your Audacity temporary folder because they are too slow.
If you have just installed a new security program, tell it to whitelist Audacity and to exclude its temporary folder from anti-virus scanning.
If you need more help please say exactly what you are trying to record and what equipment you are using to do that (makes and model numbers).
Gale