Since it's win7's starter edition it probably runs on a netbook or something with probably has a slow cpu (atom).
You could slash in the start up programs but I don't think it will do much difference.
Can you detail us you gear ?
It's an Aspire One Netbook.
I've slashed the number of programs starting at startup to a point less than it had been before the problem arose. It's made no difference.
I've checked Process Explorer which is telling that Micorosoft's Security Essentials is using alot of resources. I had Clam Win prior but downloading definitions (from Australia?) was always problematic.
I do not recall if the problem started after replacing Clam Win with MSE.
I've disengaged Windows Defender hoping to regain resources but the removal has made no difference.
Since you mentioned it, I recall trying a program that changes the orb that is the start button and even though I have since removed that program and restored explorer.exe, I'm beginning to think the cosmetic attempt fouled something. Like a size parameter.