f-secure anti virus ..cant uninstall it???

im with talktalk and i have laptop..windows vista......and i have there security ..f-secure..protecting my laptop...but internet went off for few days ..and when it came back on f-secure wasnt working, i rang them and they said..just uninstall old one ..and download it again...i did this..and it said it uninstalled...but its still on laptop..but just comes up saying..its exspired....apparently part of the file is missing so it wont uninstall...and ive tried downloading f-secure again but it wont finish installation..saying..i must uninstall old one ...have tried putting other anti virus protection on...but they all wont work ..because of the same problem....so now im not protected...any help would be appreciated....