Help with data insert

[Max Spit]

Hello everyone! I am using PHP + MySQL and buld websites. Recently I encountered one problem. Actually I am using CMS to insert data in MySQL, but it seems to insert only limited amount of it. For example, I have a large text, and when I try to insert it, it becomes cut. I am sure, id does not depend on CMS, but I cannot figure out, what should I change in MySQL settings or variables?
To sum up: I don't know, how to increase the amount of text I try to insert - thus it becomes cut.