Question before I start the cleaning process

Running XP Home SP3
Before I start the cleaning process I want to know if there is something specific that any of you are aware of for this problem.
The computer and all peripherals including two external HD (auto software on the external HD has been disabled and the services disabled) are shut down normally in the evening. In the morning, the computer and HD are on by themselves! I have no auto shutdown or start-up apps installed. The hard disc is quite as a church mouse with no extraneous hard disc activity that might indicate spyware/malware. Is there something specific that I could/should look for instead of a full cleaning?

My primary protection is AntiVir Personal with Threatfire. Each Sunday, I will run two of the following at random: SuperAntiVirus or MalwareBytes, then either Spybot, Lavasoft Adaware, or aSquared. My system is usually always clean.

This started only this week but forget exactly the day. There was a Microsoft Update I believe on Wednesday.

 

Sorry for the confusion. I have been working with the Hardware forum to solve the early AM apparant attempts to start the computer. We seem to have ruled out the external hard drives as teh source but still checking the boot files.

Is malware a potential source? I was thinking something like a dialer with a time setting. But my sytem is very clean. Last weekend due to this problem my first inclination was malware. I ran five different programs and found only 22 tracking cookies.

What I was asking was if there was something else I could be doing in the way of malware mitigation for a problem like this, or would anything that could case this likely to be corrected with the scanning I've done?