It sounds like your Windows operating system itself has an issue with it's start up files, like a virus, malware, adware , trojan ect.
There are a couple of avenues of attack that are available.
Some AV software will only do limited if any scans due to limitations set if you are in safe-mode so I suggest you use an E.R.D. (Emergency Rescue Disk) made from your Av software. If you dont have one made then you may TRY-IT in safe-mode, but if unsuccessful , go here and download this one,extract it and burn it to disk.
http://support.kaspersky.com/faq/?qid=208282173
Be sure your system is set to boot from a CD and boot the system with that disk in the drive.
If this doesn't help you you may want to consider a "REPAIR' install of the windows system files.
A repair install replaces only the operating system files while saving all of your data
Here is a site that walks you through it. Please read EVERYTHING in it, especially the WARNINGS.
http://www.michaelstevenstech.com/XPrepairinstall.htmIf you feel the AV E.R.Disk wasn't thorough and your hesitant about the repair install of the operating system files and want to do a foolproof infection scan to rule that out, then there are also adapters you can get so you can mount your laptop hard drive as a slave drive in a Desktop PC or another one a little more money that mounts through the USB port.
That way you can run your multiple scans there.
http://www.geeks.com/details.asp?invtid=HD-108&cat=HDD or
http://www.geeks.com/details.asp?InvtId=2020D&cpc=RESXThese adapters are also great for retrieving all of your data to save before doing a repair install or a complete windows replacement.
You have already checked a couple of the most common causes of your problem like heat & ram and this about all I can suggest so I leave you with a good luck and when or if your problem is solved let us know so your suggestions may help others.