Phenom ll x4 965 BE, a 970 motherboard and with a decent cooler.. Will that fit your budget? I have no idea of computer stores in your country..
What about an FX-6100/4100 with a 970 motherboard with a decent cooler/stock cooler if you won't overclock..
Another option is: an i3 processor with an H61 motherboard and stick to stock cooler if you want to save more money for a better motherboard.
If you are sticking with the same motherboard then you need a LGA775 processor. The one I would recommend is Intel Core2 Q6600 - Quad core and 2.4GHz.
However there is a chance this will not work with your board even though it uses the same socket. It uses a newer architecture than your current Pentium so we would need to know what type of board you have to confirm it.
If you also want to replace the motherboard - AMD is generally the way to go for value for money. And avoid anything with Celeron written on it. Something like the FX-4 4100 plus a motherboard is just under £110. Not sure how that plays out for you in $
Have you tried formating the HDD and going for a clean install?
Years and years of driver updates,video codecs and software corrupt the windows registry and mess up your OS.
The cheapest alternative would be a clean OS install then if it still doesnt perform as you like you better save some $ because as some one said it is a 775 socket mobo and a CPU for that can be extremely expensive simply because they are hard to find.
Your money would be better put on a new cpu and mobo combo that will last a few years than a "patch" that can go wrong.
For a budget, yet good performing processor, I would recommend an AMD Phenom X4 965 BE. With it's Black Edition designation you can overclock it beyond its stock 3.4 GHz AND it's only $75 at Tigerdirect.com right now. Of course, you'll need an aftermarket cooler. Something like the Cooler Master Hyper 212, which costs ~$25 at Amazon.
For really good performance, any of the 2nd or 3rd generation i5's will do (The i7 has hyperthreading, but games rarely use that). That i5-2500K/3570K are great for overclocking and cost $200 at Newegg.com (You can get $20 off from a V.me visa promo). However, if that is too much money, you can go for the i5-3470 ($180 on Amazon) or i5-2310 ($165 also on Amazon. The former will offer 1600 MHz RAM speed and better integrated graphics (but really, if you game, you should use a graphics card), etc. but costs $15 more.
hey if u dont want to change ur mobo then go for intel C2Q 8300/8400 (m not sure ur mobo will support or not - mention ur mobo)
i am using 8300, best performance for the price.
i bought that 2 yrs back for 7000 rs.
now u should get it for as little as 5k.
I recommend going with a modern Pentium like a G630 or G860 - that's what I'm doing, and I'm still on a Pentium 4! (Although I love my 4). It's all about preference though, and needs. The Pentiums though fit your budget well, and aren't too shabby - they're very close to the i3 for gaming.
you could get the fx-4300 or fx-6300 alongwith a cheap am3+ mobo or you could get an i3-3220 alongwith a cheap H67 mobo for about the same price as the amd.
so its upto you to decide to go either amd or intel. also what graphics card do you have ?