Slow restart is a new problem. Why?

I'm relatively new to Mac, working on a white iMac 24, 2.16Ghz, 2GB RAM, 250GB HDD, 256 VRAM. The computer has always booted up quick, and restarted fast when I needed to restart....I'm talking 1 Min or less. Now all of a sudden it's 5-6 minutes after I choose "restart" under the Apple menu icon in upper left. Why would this be happening?? I have some thoughts, but I'm not sure....

I recently got the MacHeist II. I've activated very few of the programs with the licenses, and have really only used one up to this point (Tiki Golf...the kids love it!). I also hooked up an external HDD about 2-3 weeks ago, but the slow startup didn't happen then.

The only other computer changes, would be a few songs downloaded, and my kids using some library software (games) on here. I have plenty of on board HDD space left (over 170 GB).

I don't know what to do here. This sudden change to 5-6 minutes startup has me worried. Any thoughts from you pros out there?? Many thanks...

Changed Startup Disk preference

For those that care or have similar issue, while looking through my preference panels, I noticed the "startup disk" had no disk selected. Weird, I'm not sure how this happened. I selected my "Mac OS X 10.4.11" version on "Macintosh HD", made sure the setting was saved, and then rebooted. Everything was smooth, less than 1 minute. I did it twice to make sure it wasn't a fluke.

I'm thinking because I didn't have anything selected in this preference, I had a kids game in the CD drive, and I also have an external, that the comp was searching around for what to boot from. It still seems odd, but I'm thinking that could have been it.

Am I on target here, or did I just get lucky for a couple of boots?? This iMac is only 7 months old. It couldn't be slow yet.