iMac boots up to an empty white screen with mouse arrow
Hello
I have a 20" iMac which was purchased back in late 2006. I've been sucessfully able to upgrade the OS to 10.7.5 Lion edition. This is an Intel Core 2 Duo processor with 3GB RAM. Every so often it will boot up with an empty white screen with mouse arrow and nothing else. At that point, I normally just hold down the power button to shunt it down and restart after a bit and it would load up everything fine. At first, I thought the problem could be with the hard drive so I changed out the drive and it didn't solve the problem. I'm pretty sure that this problem has something to do with the video card.
I was wondering if there are any video/graphics card drivers or utilities that I could install to fix this issue. Also please let me know if I can try something else to narrow down a cause for this.
Thanks.
iMac, Mac OS X (10.7.5), 3GB System RAM