I recntly bought an asus EAH 3870 TOP, but when i installed it in my computer, my internet stopped working, games were crashing, lagging and bugging up. When i take the card out, and put my old cards back in, the internet works again and games work normally.
(i have installed all drivers correctly). I have a 450 watt power supply, which is the minimum which is recomended. Anyone got any advice?

Sadly, you gave us very little to go on here.

What version of Windows?
What CPU?
How much RAM?
What is the make an model of the 450W supply?

Since we know nothing of the rest of the hardware or their power requirements, I can only guess that 450 supply is bad, or simply inadequate. It is important to understand that 450W PSU from Maker A does not equal 450W from Maker B. I would much rather have a 450W from Antec, for example, that a 500W from a no-name generic.

Use the eXtreme PSU Calculator Lite to determine your power supply unit (PSU) requirements. Plug in all the hardware you think you might have in 2 or 3 years (extra drives, bigger or 2nd video card, more RAM, etc.). Be sure to read and heed the notes at the bottom. I recommend you set Capacitor Aging to 30%, and if you participate in distributive computing projects (e.g. BOINC or Folding@Home), I recommend setting TDP to 100%. Research your video card and pay particular attention to the power supply requirements for your card listed on your video card maker's website. Then look for power supply brands listed under the "Good" column of PC Mechanic's PSU Reference List. Ensure the supplied amperage on the +12V rails of your chosen PSU meets the requirements of your video card. Don't try to save a few dollars by getting a cheap supply. Digital electronics, including CPUs, RAM, and today's advanced graphics cards, need clean, stable power. A good, well chosen supply will provide years of service and upgrade wiggle room. I strongly recommend you pick a supply with an efficiency rating equal to, or greater than 80%. Look for the 80 Plus - EnergyStar Compliant label. And don't forget to budget for a good UPS with AVR (automatic voltage regulation).

_________________
Bill, AFE7Ret
Freedom is NOT Free!