my website was working properly till yesterday or i didn't come to know this issue..

i haven't made any changes in anything since i updated my core to 1.5.2 and rest plugins

when i or someone open website there is a 70% CHANGE IT GIVES 500.phtml ERROR , 

and by my computer if i am logged in as admin and if 500.phtml error comes and i refresh page  it keep redirecting me to installation page , after it i have to close browser , clear cache , and have to wait. 

i am really scared if my all users getting this  installation page , it will be a big trouble for my website n security 

please help asap 

i enabled debug mode i then checked error log 

it gave me fallowing errors

Wed Apr 17 05:59:27 2013] [error] [client 115.240.99.112] Failed loading /usr/php/53/usr/lib64/php/modules/ioncube_loader_lin.so: /usr/php/53/usr/lib64/php/modules/ioncube_loader_lin.so: undefined symbol: zend_resolve_path, referer: http://www.yourmatesgroup.com/ ;

[Wed Apr 17 05:59:27 2013] [error] [client 115.240.99.112] Failed loading /usr/php/53/usr/lib64/php/modules/ixed.lin: /usr/php/53/usr/lib64/php/modules/ixed.lin: undefined symbol: zend_dirname, referer: http://www.yourmatesgroup.com/

[Wed Apr 17 05:59:27 2013] [error] [client 115.240.99.112] Failed loading /usr/php/53/usr/lib64/php/modules/ZendGuardLoader.so: /usr/php/53/usr/lib64/php/modules/ZendGuardLoader.so: undefined symbol: gc_remove_zval_from_buffer, referer: http://www.yourmatesgroup.com/