I got home last night, and my iMac screen was all white with even light grey bars running vertically, about 1 or 2 pixels in width and a constant ~1 cm apart for the whole screen. I tried alt tabbing, option command escape, sleep shortcut, turn off shortcut, everything else I could think of or found on the web, but had no success, so I ended up doing a hard shutdown by holding the power button down. I'm also running online backup (CrashPlan), and before last night, I had a bit under 60 GB left, but this morning I checked and I have 194 GB left. The amount backed up has dropped heavily (now 300 GB instead of ~450 GB), but my backup space seems to be the same (390 GB). At this stage I'm wondering whether my harddrive has had a bit of a crash and there's been corruption. It's working fine this morning, and I ran a repair on the HDD and it seemed all fine. Any ideas?