Bing dropped homepage from serps

[bjwillis]

Have noticed big ranking drop in BING, previously number 2 now not in top 100? have checked with site: and it is listed however, our homepage is not listed only /index.html. The homepage has PR 2 and used to be listed - I am guessing that this is why we have dropped - am I correct? If so, why has the homepage been dropped.
Google and yahoo still showing in results.
any help appreciated.