Can my roommate change the locks lock me out and keep my stuff because I was only able to make a partial rent payment!
1 attorney answer
If you were both co-tenants, your roommate would have no right to evict you at all - only the landlord could.
If you were a subtenant, the roommate still could not lawfully lock you out or engage in similar "self-help" (see e.g. Civil Code Sections 789.3 and 1940.2), and would have to lawfully evict via the unlawful detainer process.
You should complain to the police - they sometimes intervene in illegal lockout situations. If you are a co-tenant, you should also complain to the landlord, and ask for a key to the new lock, etc.
You could also sue your roommate either in small claims court (usually up to $10k), or by hiring a local landlord-tenant attorney.