My computer has a bootlocker
I have tried to bypass it but if i did, windows wouldn't boot anymore.
If you mean a dual boot.... Install Ubuntu next to Windows 8 (UEFI dual boot)
If by 'alonngside' you mean running at the same time, you might want to look into virtualbox.
I installed ubuntu on my pc alongside windows Vista
When I choose to boot ubuntu the PC doesn't run. Can anyone help?
You can try Boot-repair. Boot-Repair, simple tool to recover access to your Operating Systems. To get Boot-repair you can download it from here
Once you download the ISO file, go ahead and burn it to a CD, then make sure that your system is set to boot from CD. Boot from the newly created Boot-repair CD, and follow the on-screen instructions.