slow

ok i got a pc problem my computer runs real slow i have ran defrag avg8.5 and all kinds of stuff it still runs slow i was told my memory might be bad when i click on start it takes several seconds to open and show up my internet runs slow also i have cable internet and it runs like dial up any program i try to opens takes forever i dont know what to do can someone please help me im on a based income and cant afford pc diagnostics done by the professonials or anything like the sort any help that i could get would be much appreciated u can contact me at biggin2430@yahoo.com thank you and have a nice day