When I put my 500 pages on my website I did not know about keywords. These pages are not being found in SERPS for obvious reasons. I have started to change all of the titles by inserting keywords into all of them, but is changing page titles going to give me any problems with Google. Any help would be appreciated.
Keyword targeting in titles and description is good idea but do not overdo it otherwise you may devalue your keyword's importance. If you have any doubt about your this change, you can try Google optimizer. It is Google's tool for testing any change in your content.