IE6 & Firefox--Page Cannot Be Displayed Errors

Hi. I have a used CPU with Windows XP/SP 2 with IE 6.

Three months ago, I followed the directions on www.pcnineoneone.com to speed up my computer. That's when my problem started.

Since then, when I use IE 6, I get a "Page Cannot Be Displayed" error almost every time that I:
(1) go to a secure site, such as clickbank.
(2) click on a Google ad.
(3) click on any link from Goodsearch search engine.

Also, I see the same error where ads are supposed to be on other pages, such as Yahoo homepage.

I downloaded Firefox a few days ago, thinking that this might solve my problem, but it didn't.

Yesterday, when I would try to connect via IE6, nothing happened. This happened after repeated tries. I finally connected with Firefox and I've stayed connected because I'm afraid to disconnect and never be able to get back on the internet.

Here's what I've done so far:
(1) I looked through your malware removal thread and did all of the scans recommended except HiJackThis because I'm afraid of rebooting my computer and never being able to get back online. I tried connecting online in safe mode, but I never could.

I'm afraid that when I went to www.pcnineoneone.com and followed their directions, that I must have removed something necessary for IE6 to work correctly. (The directions required me to remove a lot of stuff.)

I would be very grateful for any help you could offer!

Kimberly