I switched my PC on yesterday and the monitor's LED just flashed with nothing on the screen. Everything inside the chassis seemed to be spinning etc like they do on startup but there were no beeps. Usually, I think, there's one. I tried switching it off using the ON/OFF button but it wouldn't. So, I switched it off at the back of the box, pulled the power cable out, held the power button for a minute and plugged the power cable back in. Switching on I got to the BIOS POST screen and it said something like: DSQ testing failed reverting to slower DRAM speeds. After this I get to a black screen with a flashing dead cursor. Restarting a few times and I always ended up at the same screen. On one final restart and suddenly it boots Windows and everything's okay. I use the PC and switch it off. This morning I switch it on and I'm back at square one with no video signal and no beep and unable to switch it off without pulling out the power. What's wrong and what must I do? Any help would be appreciated.