UI glitches

Hey, Im new to this forum.

A week ago my Imac (late 2009) started to show some strange UI graphical glitches. Some parts were missing and I couldn't for example see, when clicking on the apple logo, "the fallout menu" (don't know if thats the name for it). Also all the menu's of every program went black. It is hard to describe since I have no Print-screen. After a Hard-reset or good guessing where the restart button was, the system functioned normally again but only for a couple of minutes. After every reset it seemed the UI was showing glitches faster and faster till the glitches were continuous, even after a reset. I tried to do a back up with time machine (a 3 months old time-machine back-up) but the problem persisted.

I now formatted the HHD en installed a new copy of Yosemite and mavericks, both on a bootable usb. Problem still exists. The install seems to work ok. But after that im stuck on choosing a language because the rest of the buttons and all are missing. Is this a UI problem or hardware problem?

The HHD (I replaced it myself a view months ago, because the original died) seem to work fine judging by what Disk Utility says.

I add some images to show what I mean.

Hope someone could help me. Greetings, Michiel.