I can't install windows 8.1 pro n x64 - different - "windows cannot be installed to this disk gpt"

Hi,
when i've bought my laptop last summer (lenovo ideapad g510 intel 4200M 2.5GHz 4 GB RAM and AMD Radeon HD 8570m -if you want more specs just ask-) i installed windows 8.1 or 8 i don't know anymore... and then i made it dual boot with a windows 7 ultimate. Everything worked fine. In October or November i uninstalled windows 7 and windows 8.1 x86 and i have installed only windows 8.1 pro n x64.Everything worked fine, since Ianuary when i have got blue screen ( i forgot what was the problem but i belive i fixed it) in Febryary, i forgot what was the problem but i have uninstalled my windows 8.1 pro n x64 and tried to reinstall it, but at the installation advance options, it sayed something like "the disk is a mbr and on efi systems windows can be installed on gpt disks" so i installed my windows 7 again and run a partition program and i converted my disk from mbr to gpt (and i belive i had to make it dynamic or something like that) WITHOUT FORMATING the other partition (with 850+ GB with important stuff). then i reinstalled my windows 8.1 again. worked fine at the beginning then i got a blue screen "system_service_exception (from the file) atikmpag.sys" on startup and even when i shutdown it... i tried to fix it, but i managed to unsintall my graphics drivers, both and i couldn't installed my intel driver and the amd wasn't installing the switchable thing... Today i run again the setup, i got to the partition manage screen, and i deleted my partition where was installed windows 8.1 and now i can't make a new one, or if a make one with diskpart, it says "windows cannot be installed to this disk gpt"

PLEASE HELP ME, i want to make a new partition where i can install the windows fine, without formating the big one (with 850+ GB) i want to put my windows on this 100 GB partition. I searched, and i didn't find anything useful for me, i know, is much more easyly by formating the whole disk, but i have a lot of important stuff on that 800+GB partition and i don't want to lose it. i mean i can't. The big partition is "primary" and if i do another one with disk part it is primary too...i belive my computer hardware is fine, just tell me a windows or a method how i can install a working windows. AND TELL ME WHY ARE THOSE "ERRORS".

Thanks.

P.S. If you want more info about my pc or anything else that could help you to determinate the cause, just ask.
P.S.S. Sorry for my bad english.

tl;dr
1>Change BIOS from UEFI to Legacy Emulation mode, and try installing again.
2> If (1) fails or cannot be done, download a live linux on another computer, make a bootable USB stick, boot to linux live, and convert the disk to GPT using Gdisk.
READ
CAUTION: This requires some level of familiarity with UNIX commands, a CL interface, and knowledge of partition schemes-in short, it's NOT a simple Windows-like point-and-click operation. Failure to understand what you're doing, and entering wrong commands, can delete the whole HDD. Be extremely careful. If you're not used to Linux, BSD, UNIX like things, better stay away from this and ask someone who has more experience- Windows experience doesn't count while using a *NIX system, if anything, it just makes things worse, as the average user feels he knows everything and enters commands which should not be entered.
NOTE:If your live Linux does not come with Gdisk, you should make a "persistent" live USB stick and install Gdisk from an online repository before proceeding.