Vista 32 very slow boot

I am using dell inspiron running vista home premium 32 bit with 4gb RAM. My system has been booting up too slow. from the time it is turned on to a complete boot, it takes about 10 - 12 minutes. I have disabled all startup programs and most startup services except AVG antivirus. With some research, I learned to filter the event log and I learnt that the following degradation existed.
Sound driver
Video Driver
AVG resident shield
windows explorer
and many others yet to review.

I use Eusing registry cleaner and clean registry every couple of days. I run full scan on AVG at least once a week.

I would appreciate any help on this matter.