Hello sisla, and welcome to the HP Forums!
I see you are having issues with the quality of your print outs. I would love to help, but I do have a few questions first. I am linking a few HP Support documents below that will show you how to find your operating system. Also, if you're using Windows, please include whether your operating system is 32-bit or 64-bit.
Mac OS X: How Do I Find Which Mac OS X Version Is on My Computer?
Which Windows operating system am I running?
Is the Windows Version on My Computer 32-bit or 64-bit?
Also, does this issue occur when making a copy?
Please let me know what you find.