I have to write following code each time I start my PC.
set root=(hd0,8)
set prefix=(hd0,8)/boot/grub
insmod normal
normal
Can anyone tell a littel what this commands do and what is Grub? Also, how to start pc without this?
did you by change have another distro on your box that you've since deleted?
the commands you type in tell grub to use hd0 (first hdd read by bios) & 8th partition. grub consists of many parts; part 1 is the MBR or first 512 byte sector of HDD that is really a pointer to next part. this pointer on your machine is likely pointing to an old /boot partition you've wiped/reused. it can only point to one place and commonly is the last OS you installed. when your system is running, the easiest fix is to have your system re-install grub on your hdd (or in the correct places)
How can I reinstall GRUB Bootloader on MBR after installing Kubuntu?
to learn more about grub - I'd suggest the manual/doco firstly, but if web sites are more your thing try a search engine or
http://www.dedoimedo.com/computers/grub-2.html
IF you have only a single OS you can boot without grub; but its still useful if things go wrong, for example if an update or change (we make) causes kernel.panic on boot; we can tell grub to boot an older kernel, or change the params/options we made to get it to boot (eg. tell it to boot only in maintenance/recovery mode). grub is worth having unless you're sure you'll never have problems.