A500s Powering Down

Hello,
 
I've had my A500s for 1 year, the last 5 months or so being dogged with it powering down.
 
I've tried (I think) nearly everything: reinstall driver, system restore to the last period in which it worked (this solved it once), running malware and removing corrupted items, using different usb ports and cables, to reformatting my entire hard drive (I suspected a virus as my hotmail account was infected); all to no avail.
 
I'm genuinely at a loss here and desperate for any assistance you can give me.
 
Thanks.
 
Richard.