Oracle 11G Startup failed after altering the number of system processes
First you can try:

STARTUP NOMOUNT
ALTER SYSTEM SET processes=400;
SHUTDOWN IMMEDIATE
STARTUP


If Oracle cannot start even in NOMOUNT mode then you can fetch configuration information from spfile:

strings $ORACLE_HOME/dbs/spfile$SID.ora &gt; /tmp/pfile


Then edit processes in /tmp/pfile cleanup some mess made by strings start Oracle with pfile and recreate spfile:

STARTUP pfile=/tmp/pfile
CREATE spfile FROM pfile='/tmp/pfile';