Hi all! I'm a newbie, and I really need some HOPE for my laptop. <_< I'm not entirely certain if the nature of the problem makes it belong in Hardware, so I apologize ahead of time if I'm not in the right place!

My laptop is an Acer Aspire 5315, and I'm running Windows Vista, Service Pack 1 with Norton Anti-virus (And I can't stand it) and Ad-Aware. I've done a lot of virus scans recently and am pretty certain that isn't the cause of the problem.

The problem is that my computer keeps randomly shutting down without any sort of warning. And yes, I made sure my computer was plugged in, the battery was charged, and that it wasn't overheating. My experience with desktops has always told me that usually, when computers shut down randomly LIKE that, it's the power supply, but with laptops, I'm not entirely sure. At any rate, it has escalated to the point that it won't stay on for more than about 5-20 minutes, and that if I try to turn it back on immediately, it will shut down within about 30 SECONDS in the middle of loading Windows.

I've already taken it into a computer expert once who reloaded Windows after the constant shutting down corrupted it, and took it back to him again when it shut down randomly about three times after that. The second time he claimed that after leaving it running some tests for six hours on his desk, it didn't shut down once. For a while after this, the problem seemed to slow down, but suddenly escalated last night to the point that I was panicking to use the 15 minute window I could get out of it to back up all of my things because the shutting down was corrupting Windows again. I've begun to notice that the longer I let the computer sit without running, the longer it will run afterward, but I'm not entirely certain if this is relevant. I'm at a sort of loss as to what to do at this point, and if anything, would at least like a reason as to why it's doing that if it's entirely unfixable. . .

So, does anyone have a sort of diagnosis for what might be going on? Is it one of those unfixable hardware problems? Do you think it might be wise to attempt to load an available copy of Windows 7 that I have on it to see if it's just Vista itself or something? Any help is greatly appreciated!1.  To rule out the hard drive and all of the software that it contains; boot a "free" memory diagnostic from CD and let it run a few hours.  If you still experience random shutdowns, you'll need to look at:
     a.  Heat
     b.  Power
     c.  Hardware

To minimize the hardware configuration, you could remove the hard drive and battery from the laptop for these tests (as the memory diagnostic doesn't REQUIRE them).

2.  Memory Diagnostic.  Download the "free" diagnostic software at either www.memtest86.com  or www.memtest.org  and create the desired bootable media.  Boot the program and let it run indefinitely ( key to exit).I experienced this not so long ago on a laptop and it turned out it was the memory, maybe look into that