1st, make sure that your screen orientation lock is not on. You can find that at the top of the screen. Then try going into Display, Screen Resolution, and making sure the box is checked to allow/ not allow screen orientation. This should alleviate the issue.

I have a Dell Inspiron and have had it for a year. Over the past week, when I have been using the computer it stops responding and I am unable to do Ctrl Alt Del or do anything except a hard shut down. This has been happening at least 5 times a day. It is also not shutting down now.

The issue could be due to an application or a driver as the system runs properly in Safe Mode and with services disabled in Normal Mode. Vostro 430 supports DDR3-1333MHz PC3-10600 modules and the Crucial modules seems to be compatible as per the information provided on their website.