[HELP] i have wordpress hosted on a vps

my website were working fine and then yesterday it went down due of excessive use of memory i am not sure what is the problem but everytime my visitors went high my server will go down,

wordpress version is updated and plugins i tried contacting my costumer support but it takes like 12 hours before they reply and cant even solve it, i manage to transfer my backup to a different vps but the problem is my index is blank and i have to disable all my plugins to make it work, it was working fine few hour ago and this time its down again with same problem how am i going to fix these? any opinion?

I checked my cpanel error log and i have this

[Sun May 27 13:34:17 2012] [error] [client 80.22.212.14] (12)Cannot allocate memory: couldn't create child process: /opt/suphp/sbin/suphp for /home/taendat/public_html/index.php

i see these errors on both of my vps server

Anyone? i tried disabling all my plugins but it still go down as soon as i get my traffic back

RAM usage limit reached , ask your host about it .
You can trying caching plugins like WP-Super Cache , and see if it might solve the issue.

i tried and also disabled plugins, is there other reason that im getting these? my host cant even help me im using directspace.net

Your going to have to upgrade you hosting or find abetter host if they are over selling the vps

actually i have a good specs of vps my website is running for a months with no problem like this, i tried migrating my backup on different hosting and i get the same problem is it possible that my website is attack by something?