Windows 7 HP Pro Desktop freezing + won't turn on.

[Kineas]

I haven't been able to determine whether this is a software or hardware issue so I've posted in this section.

 

We're using HP Pro 3515 desktops in our school, all are fine except for one. The desktop in question is in the main office and isn't linked to the domain so is running standalone and the office staff tend to leave it on over night on the login screen. When the staff come in on a morning, the desktop is frozen on the login screen, the mouse won't move and it's unresponsive. Holding the power button down turns it off, but when it's turned back on,the screen stays blank. The only way to get it back on is to pull the power lead out of the PSU, wait around 10 seconds and plug it back in. It'll then come on.

 

I checked event viewer which shows no errors, just shows a log of events up until say around 1am when it obviously froze.

 

I asked the staff to turn it off before they left for the day and turn it on when they get in. When they have attempted this today, it's just showing a blank screen until I remove the power lead and reattach it.

 

I want to try and determine what the issue is before ringing HP, I'd rather be on the phone with them for as short amount of time as possible. When we first purchased these a few months ago, within a week one of the hard drives failed and HP had to send us a replacement.

[Duke5A]

It's probably just a bad stick of RAM. Let MemTest86 run on it for a couple hours.

[HTCPCP]

as Duke has said, run Memtest, However if that comes back without a fault, is it that the computer is trying to put itself in sleep mode and isn't waking up again?