ok you can fix it yourself but you will need either:
CD/DVDs, a DVD/CD burner, USB flash drives, external hard drive
using anyone of the above media back up any data that is important to you e.g. music, photos, work stuff etc...
reload OS using recovery disk that came with the computer or restore partition
disk:
insert disk and restart computer press F11 or F12 at the very start of when computer comes back on, you should get a boot menu choose to boot from CD/optical drive and follow instructions to reload OS
ps. if the computer doesn't show a boot menu with F11 or F12, then enter BIOS (F2 or Del at boot up) and change boot priority there, just change it back when OS is finished reloading
partition:
press and hold F8 or F7 at the start of boot up and you should have a menu asking you about safe mode etc..., one of the items on the list will be boot from recovery partition (or similar) select this and then follow instructions
if you don't have recovery disk or partition then you will need to pay someone to fix the computer, if you can get recovery disk as it can help in these situations