Mac Mini desktop folders/icons and top menu blinking on and off

Hello. I've just returned to my Mac Mini after being away for a few days. Upon booting and having the desktop fully load, I have been experiencing all folders/icons and top menu bar blinking on and off every ten seconds. I have only opened Fire Fox to try and diagnose why this is happening. No solution yet.

I am running Snowleopard with Mavericks and I'm aware Mavericks is a little buggy at the moment (beach ball used to blink on and off every now and again and performance has gotten slow) I only have the HDD replaced last week as the last one failed. I really need to fix this problem soon as I rely on my Mac to work from home.

Any help would be greatly appreciated

Jan