ok you need a network card and the ntl disk then for the modem drivers,
going off your spec, id just do a clean up and buy a new dvd/cd burner
something like this
https://www.maplin.co.uk/Module.aspx?ModuleNo=224081
maybe in the future buy some more memory but thats if you want it speeding up.
can go through all the cleaning stuff with you, they sell dvd drives at any pc shop
as for your sound distorting, that could be your speakers, try pluggin earphones in and seeing if it does the same