[dba-SQLServer] Can't drop the PK from a table

I have a table into which a process inserts 1300 rows every 10 minutes.
Currently there are 34 million rows in the table. There are 7 indexes on the
table, two of which are seriously fragmented (98% and 87%). I ran dbcc
reindex on the table and it changed the fragmentation not at all. Why would
that be the case? Another thing that puzzles me is that one of the
fragmented indexes is the PK clustered index and the PK as is int identity.
Also, I find that I cannot drop the PK index, which I thought I'd do as a
way of rebuilding it from scratch. When I try to drop the index and save the
table, the system times out and won't let me do it. Any idea why this might
be so?

Arthur