Dell Inspiron 5100 Cd Drive Problems / Hence Windows Install prevention

Hi, thanks for taking the time to read my post.
I was given a old/used Dell Inspiron 5100 by my fiancée family as it was just sitting around and they said it wasn't working properly. So I eagerly accepted the challenge to try and fix it...No luck so far!...So please help!

The XP OS wouldn't boot properly for some reason, so naturally attempted a clean install. Unfortunately the CD drive isn't working. (Tried changing boot options in bios-nothing!) It has it's light flashing, but does not read any discs for some reason. Any ideas or guide for fixing cd drives are much appreciated. Ultimately, If I can't fix the cd drive, then with it networked, I can live without it. I can't network it till I get XP sorted..so a vicious circle begins!

I removed the HD and put it in a friends Dell laptop,re-installed windows on it and it worked perfectly on their machine, transferred the HD back to the laptop thinking it would be fine and again it wouldn't boot. The BIOS sees the drive but just doesn't like it for some reason.

So as I said above, if anyone knows any easy/quick fixes for this cd drive then please let me know, otherwise I need some advice on how I can get a clean install on to HD which is actually performed on that laptop, so I know it will boot. Can I perform an install via a networking cable without being able to access windows?. If so, please advise how? Also If I was to consider a external cd/DVD usb/firewire drive, are these bootable?...In other words, am I able to install XP from a external drive from within DOS or configure the BIOS to find the external drive etc.? Or anything else I haven't thought of, please feel free to shout any suggestions.

sorry for being so long!...thank you in advance for your time and help...

Firstly thanks for posting!

I will try the things you suggest,although i don't think its a matter of a dirty drive,as It doesn't seem to spin the discs, even though there is power, as opposed to an actual read error I mean. I know how to check the boot order of the installed components in the bios, but what i really wanted to know is if an external usb/firewire drive would be recognized/work in just the bios as i obviously can't get into windows to use it.

Also any advice about installing windows through a network cable?

Failing all those things, then I will try and replace the cd drive,but don't want to do that until i know that is the one and only culprit!...otherwise i might have to go with your suggestion of tossing the things, but would be a shame.

Any and all other comments welcome..thanks!