hmm..I kind of guessed this when you said users cudnt connect..
Please check the following..(some of the stuff u wud have already checked..but anyways..)
> on System task manager check how much of CPU and memory SQL Server is consuming..
Is there any there process consuming CPU/memory... If nt wats overall usage and SQL'susage..
> Check the number of connections using sysprocesses. Also check how many are on runnable state.
how many are sleeping. USing last batch column check how long they have been sleeping.
> Check whether are there any queries that are blocking either using activity monitor on SSMS or using
query provided here :-http://strictlysql.blogspot.com/2009/07/check-currently-running-statements.html
> using perfmon check the values of the following counters.
Physical disk . avg disk queue length
Processor queue length
SQL Server Locks -> Average wait time
Buffer manager obj -> Buffer cache hit ratio
SQL Server memory mananger -> Total Server Memory
Target Server Memory
I believe u have set max number of connections ServerProperties ->connections ( default setting of 0 )..