PC only boots ocassionally; vertical artifacts on monitor

Hi

I have two problems with my computer (5 years old).

When I boot my PC it usually crashes at loading the operating system (GNU/Linux, when processing the udev events to be precise) OR doesn't boot up at all. The problem occured for the first time some months ago. Firstly it happend only occasionally, but by and by it occured more and more often. By now it usually takes me up to 30 mins until I have booted successfully.

I have drawn a flowchart diagram of my boot problem; since I find it hard to describe it with words only, I hope that is all right.

Link: http://imgur.com/YzY2Z

I suspect that my power supply unit* is conking out due to the different numbers in power consumption I have measured and some quiet sizzling noises it sometimes makes. But I'm not an expert, so I might also be totally wrong. :)

Unfortunately I don't have another one lying around, so I cannot check if the culprit really is the PSU.

Can anyone think of a different reason?

• be quiet! Straight Power 700W

Life time according to the manual: 100.000 hrs (24/7 for ~12 years)

About three days ago, my PC started to print weird stuff (see pictures below) to the monitor.

I tested a second monitor and a second cable -> same artifacts, so the problem seems to be a component within the computer (video card: Asus geforce 8800 GT).

Here are some pictures: http://imgur.com/a/H5mLN#0

Any ideas on where the problem is, and how to solve it (or may it be linked to #1)?