I don't think it is your computer's problem if your INTERNET speed is slower then before. Usually ISP's have Modem pools where end users can dial and login, When one system goes down for what ever reason then they move the user accounts to another system and that could be your issue where you have been moved to 33.6 BPS modem pool. Anyways, there are few command that you could issue to your modem during dialing out which will change the modem speed. See this page for more commands:
http://www.modemhelp.org/inits/lucent.html
you should add " AT&FX&C1&D2S38=0 " to you modem's extra initialization string to boost it to V.90.
cheers