if you put your windows cd in the drive, turn the power on and during the first few seconds you should at some point be asked if you want to boot via the cd if you dont get this option you need to go into your bios to change the way you start up. you need to start up with cd drive first. bios is diffrent on all pc's but mines for example. during the first few seconds of start up you should see some writing on screen? at the bottom it should say setup or something simular. and it will tell you what key to press. normally Del key or F1 when u hit the power button just keep tapping the Del key if it loads up in bios. you will have to have a look through the tabs to find what u want but you are looking for the way the pc boots up, you will probably have HDD as primary just change the to CD-Rom

if you find all this and save it (F10 Normally) re-start pc and with cd in drive it should ask if you want to boot from that hit any key to boot from cd. you should then be procented with the windows cd recovery console. try that, if that dont work and you have no data on pc you dont mind losing for good re-format