Cannot allocate memory: couldn’t spawn child process:

Try running install.php, thats what i got fews days ago, been trying to find out myself browsing wordpress support and google, I’ve talked to my host and they said they fixed the caching/memory problem.

My error log says: Cannot allocate memory: couldn’t spawn child process: on index.php

Database is intact, i have a backup but it wont work, i tried to click install.php but i was afraid to continue, i noticed that one new user was added as admin in my database which i deleted already, which i think is due to the default page showing to install wordpress.

I need help as to where to start checking, or any suggestion what are the other possible cause.