hp printer

I have an HP Deskjet 2755e printer which I have been using for the last 6 months. But recently I am having a serious issue, sometimes the printer prints crooked. I have no idea why this happens. Could someone please help me to fix the issue?

I know this sounds stupid (and it might well be) but there is a reason for me wondering and asking. I have recently bought a lovely old DesignJet 500 and generally speaking it works very well - and until such time as I get through the many genuine cartridges I have, I am not going to mess...