[Dolly_Dimple]

Quick brief.
My laptop is around 5 years old and runs on Vista.
A few months ago, i had a massive virus that took a while to sort out and had to be sorted via another PC as the virus took over my entire screen and wouldn't let me do anything with it.
Since then, my laptop is so slow to boot up, its unreal.
Once it has booted its pretty much ok, however it does sometimes creak in use and i have to reboot it.
The other day, i ran my anti virus on it, which picked up and deleted a virus. I then ran my anti malware programme which picked up nothing.
I then cleared the cookies and defragged it.
This hasn't helped the boot up problem.
Now, when running programmes, it is slower than the other day when i de-virused it. It ran pretty quick when browsing, but now a couple of days later, its creaking a little again.
I hoover the fan regularly too.
I dont download things and the only stuff on it is what was already installed when i bought it, with the exception of Itunes.
There is more free space and memory than i can shake a stick at.
Idea's please on what could be wrong and how to speed up the boot up time.
Thanks.
PS i am a complete biff when it comes to computers, so please can any expanations be done in simple terms.