This problem is some what complicated. I am using Windows XP SP3. When i start my computer if it makes it to the log on screen. Windows will boot up fully but after time (2-6 hours), I will need to do a hard reboot, shutting down windows fails as it stalls at the log off screen then i need to either hold the power button or shut down using the power supply switch. To describe what is happening while windows is crashing, I will not have the capability of using the internet such via Firefox or Explorer and at the same time anything that needs internet connection will not even open like Firefox or Explorer or any apps like Diablo 2, Sim Societies ETC.. As time passes i will not be able to open any movie files or music files, or any apps period. Then background stuff such as Mcafe, Ad-Aware.... Then windows will go down fast after this period to leading to a hard reboot.1 person needs an answerI do too

the situation suggests to me that you may be running malicious software that gradually create resource hogs. download and run windows malicious software removal tool ,also if you dont have a good antivirus, download Microsoft security essentials.both tools are free, just bing it or visit microsoft download section