I recommend for brands of PC, ACER or Dell (xps). I wud avoid ADVENT or Median due to the fact they put in rubbish motherboards. I had 2 advent PCs both had faulty motherboard. Thats if you want to buy a fully prebuilt PC. If you buy a barebone (case PSU RAM and CPU with heatsink and fan) try going for thermaltake cases or coolermaster or antec. Motherboard ether asus or gigabyte. But its luck with barebone, or buy the full PC, thats why i like building from scratch. make sure you get a good quality PSU as it is the most impotent component in your computer. (No the CPU isnt). as it powers all your PC parts. If thats gives out faulty voltages it could break some of ur PC parts.
EDIT: for video cards well i cant recomend ether ATi or nVidia but for sub make
Ati: go with sapphire or HIS.
Nvidia: XFX, BFG or EVGA.
EDIT 2:Same with AMD and INTEL, i recommend quad core with that.