Hi,
Seriously- I had the weirdest thing happen a few weeks ago....
I had been seeing a "No Operating System" error when starting up, quite a few times, I tried various things to see what would fix it...taking the RAM chips out and reseating them seemed to allow normal operation, when nothing else, not chkdsk, nothing...would help.
I figured I would be buying some new RAM modules pretty soon...
But, it happened once more before I got any, and in frustration, I just redid the whole computer to factory settings (I keep pretty good backups so nothing was sacrificed)---that did not help.
Now, I knew I had a hardware issue.... I poked around the internet and one result pointed to a bad IDE data cable so...I looked at mine, and sure enough, a few of the 80 wire IDE wires were nicked, and exposed the copper inside... Seems that, when I reseated the RAM chips, it moved the data cable just enough to connect the broken wires, so things appeared to work after messing with the RAM! I replaced the cable and have not had any problems since. Just goes to show you how the least little thing, something that would normally not be expected to fail, can stop you.
I work with a lot of broken, often donated, computers, and am always changing drives, so I suspect one of them had a bad cable, or I nicked it somehow. This particular machine was a find> it had taken a bad fall and went through a big window and laid around on a porch for months, I fixed it up and am typing on it now.
I've also seen some XP computers, notebooks and towers, that will not start up at all,, with a bad CDROM drive in them!
Check the cables carefully, all up and down, front and back...the hard drive's and the CD drives... replace one, try to boot, replace the other, try to boot... Remember, if you have the very fine wired 80 wire cable, you need one like that. CD drives normally just use any old IDE ribbon cable.
This really sounds like a CD drive failure, do you by any chance, have any others, could you find a good working CD drive and install it- ((Of course, to test you want to disconnect the CD drive you have in there now)) to try and boot up?
You can try booting to the same Windows hard drive, if nothing was formatted it might still boot. Sometimes, things with the boot files or Master boot record get corrupted so don't expect miracles.
Worst come to worst> You have a new hard drive, and your old hard drive, so maybe you can rescue any files back from the old one after you are running again.
There are lots of things other than this to cause similar problems, I don't guarantee it's the CD drive but it sure sounds so.