Is your needle inserted into the needle bar as far as it will go? You may have a bit of lint caught up in there keeping the needle a smidge too low. If the needle is too low the eye will miss the hook as it comes around, The needle could damage your hook if the needle hits it.
Some other things to check:
Does your bobbin thread match the weight of your top thread?
Have you dropped the feed dogs? (not a necessity)
What kind of fabric are you using?
Is your needle big enough for the job?
Did you accidentally put a stretch needle in the 301? Stretch needles are off set a bit and not the best choice for a straight stitch machine.
I hope you get it sorted out. I hate it when I want to play and my machines won't play nice!