Don`t know if this is any help but...
There was something in PCA a few months back - one of the letters I think - and the problem was similar with an answer that memory was playing up.
I have, very occassionally, had broad black/white vertical stripes which I am told is something during the boot trying to write to graphics memory. Seems (from memory) to have happened when I started the external USB HDD at the same time as booting the PC.
You could try running MemTest to see if it shows up a bad or failed sector, or you could remove/replace the memory in case its a bad contact.