imjustavoid The "already running" error has a master thread here:
[CURRENT ISSUE] Sims 4 already running | EA Forums - 11818313
Please try the suggestions in the first post even though you're not currently seeing that error, as the game failing to open at all can have many of the same causes.
If none of that helps, please provide a dxdiag. Click Windows key-R, enter dxdiag in the run box, wait for the scan to finish, click "Save all information," and save the file to your desktop. From there, you can attach it to a reply using the paper clip (Attachment) icon included with the other formatting buttons.