database error

[renovatio_2143]

hi I've been experiencing a problem with my database for quite some time now.
Every now and then my pages/posts return a 404 error when visiting the site. On my wp admin panel none of my posts or pages are being displayed as well or at times categories/tags are the ones not displayed.

This problem is intermittent, so you may or may not experience it when visiting my site. Google webmaster is also showing these 404s on its crawl errors.

Im still having a problem with my contact forms not being able to send mail but my threads have already been closed, I hope you wont close this one without a solution. Thanks.

[renovatio_2143]

I reinstalled wordpress again in an attempt to solve this problem. When I imported my backup, categories and tags were missing so I had to redo them. But now I'm seeing Error establishing a database connection error pages again

[renovatio_2143]

again it fails to attach categories and tags to posts