Database is not accessible as transaction log file growing to full
First things first, if you need to kill the active user(s) immediately and make sure no more connections are made, you'll want to put the DB in single user mode.

ALTER DATABASE MyDatabase SET SINGLE_USER WITH ROLLBACK IMMEDIATE


Second you'll need to address the SUSPECT mode and hope it's an easy to fix file access issue.  Try these suggestions to fix your SUSPECT mode

Once that is fixed, do what you need to do with the database - CheckDB, backup, etc.  By keeping it in single user mode other users, including applications and any other user but you, will not be able to access the database.

To put it back in multi user mode use 

ALTER DATABASE MyDatabase SET MULTI_USER


EDIT - I should say this does not resolve why you have an ever growing transaction log.  If it is of concern, you should try to resolve that prior to killing an active transaction with sp_whoisactive, monitoring tools, etc.  But don't let the log fill the drive or it will kill the transaction anyway and roll it back.