Insufficient system resources, exception unknown software exception, or out of memory errors.

Hi experts,
I am using Windows XP 2002, and service pack 3 (bit 32).
I was running it about 8-10 hours, after that it was showing EF open error, insufficient system resources, exception unknown software exception, or out of memory errors.
But the pc would not freeze; the start menu icon would go blank. Also it won't start the task manager and some programs won't start at all. Then it needs to restart and then it is running very well for some hours.
I have installed Spybot and Avira Antivirus. Before this problem, I ran MGTools, Combofix, CCleaner, and also running some online scans.
Still I am getting this problem and now it is occurring more often. Is this a hardware problem or virus problem?
I need to solve it. Need your suggestions. Please help me.
Thanks in advance.
