Error establishing a database connection wordpress
I running a wordpress website in 512 MB Memory / 20 GB Disk /Ubuntu LAMP on 14.04,everything working fine for 2 weeks,then suddenly appear Error establishing a database connection this is what I try to solve this problem
1) increase server size to 1GB memory,still the same
2) increase swap,still cant solve
Now I cant even go in phpmyadmin,it show
#2002 Cannot log in to the MySQL server in my phpmyadmin page even my username and password is correct.
Please suggest me a solution to solve this,cause I really dont want to configure the whole server and build the site all over again.