HP G6031ea very poorly

Hi all,
I'll start at the beginning. A couple of times in the past my laptop has suffered a spat of BSODs which have been solved by reinstalling the drivers from the HP website. However, this time I haven't been able to find a definite cause or solution. A few weeks ago it started freezing, especially on startup, when left absent whether it had been on the screensaver or with the lid down, or when it was busy (opening a couple of programs at once). Normally the taskbar would become unresponsive first, followed by the programs then finally the cursor would freeze terminally. If caught in time it would shut down normally but if you acted too late it could stay frozen for however long I left it (at least an hour), or sometimes there'd be a BSOD with errors "Kernel_data_inpage_error", "Kernel_stack_inpage_error" or "IRQL not less or equal". The accessing-hard-disk light would normally stay on throughout. I can provide more info about any of these if required. Possibly because of the many enforced shutdowns, it began having trouble starting up. With both Windows and HP recovery tools it has scraped through this far but it's pretty much unusable at the moment as even when it works it will eventually freeze (generally only if you ask too much from it, but 'too much' is pitifully low) and this now means it won't restart without some hard work. It's been through the full works of Windows recovery options though.

Things I've tried include:
*Used HP recovery to return it to factory condition, no change. I've just done this again to try to make it startup.
*Reinstalled the drivers on HP's site, no change.
*Used memtest and Windows memory diagnostic which found no problems.
*Used system restore to restore to previous points. I couldn't restore to before the problems started as apparently no restore points had been created. I have no idea why this is as it was set to do so regularly Anyway, it made no difference apart from enabling it startup in one of its more broken phases.
*Completed a virus scan yesterday using avast which came up all clear.
*Defragged the hard disk to no avail.
*Safe mode makes no difference.

Things which I haven't done are:
*Checked the running temperature or cleaned out the fan. I don't want to do this myself as I haven't got a clue about the insides of computers and I'd probably yield a can of compressed air with as much finesse as a lumberjack does an axe.
*I don't think the hard disk has been checked but I'm not sure what to use to do this. Windows has certainly checked some of its files when startup has failed.

I've tried to troubleshoot myself this far but have run out of ideas. If anyone has any ideas about what might be the problem then please say now Failing that it's going to have to go to a computer repair place to see what they can make of it. Thanks anyway for reading this far, if you make any inroads I promise I'll love you for evermore

EDIT: Sorry I can't post the specs because it won't startup at the moment and I haven't got a clue without reading it off the screen.