VW Polo 2003- Won't go into second gear

As of driving today my 2003 Polo 1.2 will no longer go into second gear (possibly due to over-revving- going from 4th to 2nd?); when I try to put it into gear it crunches badly then pops back out.

Any thoughts on what this could be? I can still drive seemingly OK by shifting from 1st to 3rd, is this safe?

Thanks