"/" is a Site Collection as well (called the root Site Collection). Check the ULS log to get the full error. The Technical Details will have a Correlation ID as well as time you can correlate in the ULS logs.

the error tells us that something wrong with your root level site collection.

from Central Admin view all site collections, select your WebApp and then see if "/" site exist and also from configure quota and locks...make sure this site is not locked.

also check the ULS Logs and Event logs and share the error As Trevor Said.

i check from collection ID

please recommend for my error

Looks like you have an RBS-enabled content database. What level of access does the user spadmin have in SQL to that content database?

thank you for everyone

i add db_owner for service account