Welcome to Tom's Hardware, @Dawid!
Go into BIOS and check if you have properly set the SATA mode for the SSD to AHCI.
Did you format the SSD beforehand? I'd suggest you delete all the partitions through the Windows installer and create a new one where you can simply install Windows 7
. Can you also share more details about your system? Another thing you could try is selecting the Repair Computer options in the Windows 7 installation media and use the Command prompt's DISKPART to format the SSD.
Keep me posted if you encounter further issues!