Hello ! first, sorry for my english. I can’t acces to my bios. I want to boot from a iso cd to try an other distribution, but i don’t know how to do it. I tried with yast, and manually with “menu.lst” in grub, but it doesn’t work. When I reboot, I start on grub without bios. I hope someone will help me 
You don’t offer much info. You will find that you’ll receive answers more quickly if you do :). People reading these forums don’t like to guess - writing answers while guessing means more words and more time spent on items that could have been answered with just a line or two.
UEFI equipped PC (usually a PC of newer model - newer being approx. autumn 2013):
Normally you can hit a key a boot time to access a boot menu, where you can select the source to boot from. This is often <F12>, but I’ve also have come across <Esc> and <F2>. Your computer may even use another key for that. You need to look up your PC’s documentation or experiment for yourself. If you cannot find it, you can usually also do as shown below.
BIOS-only PC (older PCs):
You need to enter your BIOS setup and change the boot sequence, make the CD/DVD drive the topmost boot source. You press a key while booting - some PCs allow for this kind of entry only after a full power-off, and you press the key very early after power-on. How early will depend on your PC - experiment or read your PC’s manual. The keys to press, usually are one of <F1>, <F2>, <F10>, <F12>, <Esc> or <Del>. I haven’t seen <Del> being used on any PCs but Dell PCs, though, but it isn’t used for all Dell computers. However, I don’t disregard the possibility of other brands using <Del> as a BIOS entry key as well. Still other key options are imaginable, so you may need to experiment, although the keys listed are the most common alternatives in my experience.
Good luck!
dayfinger