What to do when the computer dosent boot but says no memory on the monitor

[castii]

please can some one help me what to do when the computer dosent boot but says no memory on the monitor?

 

[legendkiller]

Have you dont anything or touch anything because every time a person touches a memory stick and took it out and put it back in and after few hours of forum, finally figured it was the memory that wasn't put in properly...