Something's gone horribly wrong

Hi.

I have an 8 minute score for string orchestra. I did something to it which caused the 2nd violin part to become badly corrupted - too many beats in bars, bits repeated randomly, just a mess - and so I opened a new document and deleted the part in its entirety from EDIT>INSTRUMENTS. Then I put in a new 2nd violin part and copied it over from the previous version, but without the mutilations. This is working fine, but the new 2nd violins part now no longer shows up in PARTS: it just isn't there.

Any suggestions welcome.

Thanks very much.