sql server 2005 srvice pack 3 and 4

I am working in a company with 3000 windows server 2003 with sql server 2005 installed; we have some thing like atm devices that read record (information about buy) from sql server and people purchase mony from that device; idea was that we must install sql server service packs to better performance to read records from sql server; but after install packages all off servers become slower than past and now we can not unistall packages; what we should do? Please help us; thanks:-(