Need new computer

[tricky]

Hi guys hope you can help me out here, i'm at present using a windows based 1.8 g pentium M laptop with 1 gig of ram which up untill now has served me rather well, but lately i have been using a lot more plugs and im finding that it's starting to struggle, pops n clicks and finaly a crash. So can any of you guys sugest a replacement desktop processor configuration that will give me a substantial improvement, i cant afford an i7 at the present time, my budgrt is £500.00- £600.00. Or does anyone know of any base units, also would increasing my ram in my present setup realy make that much difference. cheers