Update: Problem Resolved Thanks for your suggestions and help. I have been lazy, and I know from the HDD replacement and one open prior to that.. that it takes effort to open these cases...well not really, but its the part about removing and replacing the LCD unit and it's recessed screws.... Finally I decided to open it again and to my amazement...one of the wire clusters was unplugged from it's circuit board. I knew it wasn't the HDD all along, as this thing hardly draws any more power then the old noisy one. I'll call them clusters, cant think of a better name right now... There are 5 wire clusters for the Backlight/LCD combo unit in the November 2006 model iMac. The main ribbon cable that supplies the LCD panel with picture, and 4 separate clusters of wires (for the backlight panel I presume). Two of these four for the backlight consist of just two wires each and another two consist of 5-6 or 7 wires each (don't remember exactly). One of the two-wire'd ones (the bottom one) was simply unplugged from that board I mentioned earlier. I'm guessing under that board is the transformer for the backlight power. This basically explains why the bottom part of my LCD wasn't as lit as the top..simply wasn't getting enough juice for that part. Why it started bright and then dimmed automatically (when it wasn't getting power there in the first place) is beyond me..but it is fixed now and back to the crisp 100% brightness it's has for 3+ years now. I have also heard of people receiving iMacs that come from the store or factory with dim areas on the LCD. I'd recommend this solution to anyone who has this problem as well. Its possible during manufacturing that a wire wasn't fully plugged in. Mine was of course my own fault; a simple overlook in a simple HDD replacement, not double checking that everything is seated/plugged in. But during manufacturing it's not impossible for them to make mistakes either. --- Orignal Post --- Well, I recently got that 750 GB HDD and installed it. I have taken my iMac apart once before to get dust out of the bottom fans which helped with overheating problems, but this time I dig slightly deeper to replace the HDD with this new bigger 750 GB. (The heat sensor part on the HDD was rather interesting) Now..I'm no barbarian when it comes to this machine, realizing how delicate it took me a good hour and a half at least with this machine making sure I was taking the utmost care when working inside if and removing the LCD panel. Well, it was all successful, I now have a huge chunk of digital world to put stuff on. But there was one small problem about 1 second after re-power up and just before reinstallation of Tiger (no leopard, i don't have it). The bottom of the screen isn't bright anymore!!!! You can see from this picture mostly the bottom left shows up as brownish yellow and washed out...taken from my 2nd gen LG Chocolate phone. http://i50.tinypic.com/2q1ifjl.jpg Well, what do I do? I only ask this because I know the screen isn't busted, because when I power the thing up, the screen is at normal healthy brightness, then it jumps the brightness down in that corner/bottom of the screen automatically and just stays there unless I restart, and watch it repeat the same process..just goes back dim again. EDIT: If it helps some... I didn't have the patience last night to update OS X, and over the years of having this thing (since Nov 2006) I have noticed LOTS of firmware updates. Now, since I have reinstalled I have version 10.4.7 (I will update later) and I wonder if a problem with the firmware updates.not being updated has something to do with it? I mean... it does go bright, brighter to normal and then bam its dim again.