Requiring a Boot disk to start

i recently got a mac. while in the process of moving some files over i though i would speed things up by using a external hard drive, since usb is 480mbs but my network is only 100mbs. anyway, connect the hard disk, copy some files on to it, and then i get an error saying i/o failure. bit weird, so for some reason i decided to do a check disk on it. now this is where everything started to go wrong i think.

the check disk said it needed to use some part of windows which it couldn't currently do. so it asked if it wanted to schedule to do the check disk on start up. so i clicked yes, not thinking much of it. anyway on restart it came up with a boot error. said something about wrong disk, and remove all attacked disks (something along those lines). anyway, after a few more restarts i decided to remove the external hard disk. now the error changed to require a windows boot disk. this was driving me made by this point. anyway, i went to enter setup and change the boot order to start with a cd-drive, and put in the boot disk. it started up fine. i turned my comp on this morning after taking the boot disk out the night before, and i got the same error i got yesterday. stupid thing! so now i need a boot disk in to start my computer...

Could some1 help me please!

(on another note, the external hard drive refuses to work at all now)