Having trouble to boot linux on my 2011 hp laptop

I have been having trouble with this for a long time but i thought that the linux mint community can help me.I have an old hp 620 that i will upgrade but for now i juts want to boot linux(i am using mate) but even after installing it it still says "Non-system disk or disk error replace and strike any key when ready" but i have it sothat it boots the hdd first i have gotten it to install it to the hdd manually and the files are on the hdd and the hdd shows but it doesnt boot please help me(and yes i am a rookie)