Corrected FSB, now K7N2 won't POST - Need help!!

Question

AMD XP 2600+ TBred B Core
1024 (2x512) MB PC3200 DDR SDRAM (Corsair XMS Series)
1 is C2 latency, 1 is normal PC3200.  I had them both in channel A, right now I'm just running my brand new normal 3200 stick.
MSI GeForce6600GT (NX6600GT-VTD128SP)
MSI K7N2 Delta2 Platinum (MS-6570E)
Enermax 365P-VE PSU (350W, 3.3V & 5V rails have 32A each, 12V rail has 26A)
The system ran fine at the default settings, I installed Windows XP with no problems. No hardware difficulties, no overheating of any component, no lack of voltage.  Everything was peachy keen, except that my XP 2600+ was being misdetected as an 2000+ because the FSB was being set at 133.  So, I went into the BIOS and used the settings I know are correct for my processor, meaning the FSB was bumped to 166.  Saved the settings to the CMOS and exited.  Now, when my PC starts up, I am greeted with a black screen.  No POST beep, no video, no nothing. CD-ROM spins up, hard drive spins up, all fans spin up, all lights light up, but...Nothing!  First move -- Reset CMOS w/ jumper.  Nothing!  Next move -- Hard CMOS reset (1hr). Nothing.  Next-move -- Barebones boot. More nothing. I even tried swapping out the video card just to be on the safe side.  (it did nothing, of course) If I didn't know better, I'd swear it was a DOA board, except it was working fine for around 18 hours, and I heard the POST beep every time it started up, and the DRAM error 'continuous long beeps' when I first set it up & had the 3200C2 stick in the Channel B slot  (which I can still hear if I try booting with the RAM removed).  I found the "Insert" key trick, but it looks like my keyboard isn't even getting power.  I've been completely unsuccesful in trying to undo my move to the 166FSB, and it seems this total failure to POST w/ this motherboard isn't a unique problem. Any help at all is GREATLY appreciated, as well as any explanation as to what in the HELL happened. This has left me utterly flummoxed. To reiterate -- my computer is in barebone state right now.  (Motherboard, gfx card, processor, RAM, all power and case connected to mobo and gfx card, nothing else) Thanks.  -David

Answer 1

... I have just experienced the very same problem as HorizonX!  I'm using a AMD Athalon 2600+ processor in an MSI K7N2 Delta 2 - LSR mainboard with 2x512MB PC3200 DDR RAM chips and I decided (don't ask me why) to switch my front side bus frequency from 166Mhz to 200Mhz.  Immediately after making the change my system, which had been working fine for about a month prior to this, failed to post - no beeps only the whirr and click of the hard drives starting up. 
I attempted to clear the CMOS by moving the clear CMOS jumper to the "clear" position for a minute or two with no results.  I then removed the battery and again set the clear CMOS jumper to "clear", this time for about five minutes, but once I returned the battery and the jumper to its original position the system still failed to post.  I figured I must have fried my CPU and was ready to start shopping for a new one.  Luckily I came across this discussion forum.  After reading the previous comments about how long mainboard capacitors can hold charge I decided to try clearing the CMOS again using some of the forum suggestions.  I unplugged my system, removed the battery, and moved the CMOS jumper to the clear position.  I then toggled the power supply on and off a few times along with the front power button and then left the system to sit for a half an hour.  After the half hour I toggled the power switches a couple of more times before I reconnected the power, reinstalled the battery, and restored the CMOS jumper to its original position.  This time IT WORKED!!  My CMOS was cleared and my system posted with default settings.  Incidentally I did look for the FSB safe mode jumper on my mainboard but it doesn't appear to have one.
Unfortunately this my not be much help to HorizonX but I just wanted to let the other contributors know their advice helped solve my problem.