My computer is about six months old. I usually keep it running almost all the time. However, if I cut it off and it sits through the night (and the place is not cold or anything, just not hot) when I start it up in the morning, there is a 50% chance it will freeze while loading Windows XP. But if I push the button and cut it off, restarting after about 30 seconds, it never fails to come back on, and everything is great.
this one smells of hardware going bad, quite possibly in the power supply. but, it could also be on the motherboard. electronic parts do wear out with use. as they do, some of them lose their original electrical integrity and begin to do odd things. heat and cold will start to affect them also. when your machine is on and you reboot, the components are already warm from the electrical current. when you let it sit over night, the parts cool down. when you warm parts up they tend to expand and can change conductivity from when they are cooler and a bit more condensed. and it's not as rare as you might think. we've seen it before on this board. the last time it was a capacitor in the power supply or motherboard, as i recall.

i've also personally experienced this on an older machine. it would take anywheres from 1 to about 15 attempts with the power button for the thing to actually boot up.

as to why it's occurring after only 6 months, you partially answered it. you keep the system on almost all the time. normally, this isnt a bad thing, but if the components were a bit flawed during manufacture, then their life expectancy will be quite a bit less.

the only way to truly test if all this is correct or not, is to take it to a shop and tell them what's going on. the downside to this is that these can sometimes be hard to detect and murphy's law says that every time they try it in the shop, it will boot up normally.

off hand, i'd say if it's only 50% of the time on a cold boot that it fails, dont worry too much about it for now. if it gets worse, and it most likely will, then go ahead and let a shop technician look at it.

there is also one other condition i am aware of that could cause this, but not really with a 50% regularity, and that's a software problem, usually some little glitch is windows during your boot sequence. but those tend to be more rare than 50%.

intermittent boot-ups on a cold boot but not a warm re-boot, tends to be hardware going bad, usually a circuit board or power supply item. so, keep an eye on it.

K.