Can't download

Recently, I was browsing on the internet and a pop up ad appeared informing me I need to up date Firefox. I had the official logo, so I thought it was legit. I clicked download. From that point on, I lost my original Firefox and was prevented by " something " to re-download it. Avast Tech Support could not remote my computer to figure out what was going on. " Something " was blocking them too. They recommended removing my data with a flash drive and re-installing Windows Microsoft with an installation disc. They could then help me out from there. Is this my only option? Those discs are pricey

Edit: Moved topic from XP to the more appropriate forum. ~ Animal

via Bleeping Computer Last 20 Posts http://www.bleepingcomputer.com/forums/t/509370/cant-download/