No harddisk detection or cdrom

1)If any cd or dvd is there in the cd or dvd drive remove them first then try booting
if problem persists then
2)check the boot device priority in the BIOS menu,change the boot device priority if required(change to 1 st boot device floppy, 2nd harddisk drive,3 rd to cdrom drive something like this)
to go to bios setup press del or f2(it depends if del key doesnt brings you the bios utility then press f2) at time when you switch on the pc ie at the time of booting the pc ,
if problem persists then
3)check whether the harddisk is detected or not in the bios setup
if it is not detected then just open the CPU & check the bus & power supply cable connected to the harddisk remove them & reinsert them ...
if required then replace with the new ones ....
if the problem persists then
4)the operating system might have got corrupted just reinstall ....
if problem persists then
5)the harddisk partitions might have got corrupted or crashed ,just try partitioning them again and by installing the operating system.