What's the browser? What are your internet download speeds? How many tabs have you got open? Is it for loading a new tab, or switching to an already open/existing tab? Do you clear cookies/cache/history on a daily basis? Do you have lot's of add-ons running? Are other programs also running/starting very slow? Questions questions.... CCleaner is a very good program for clearing stuff up. I've got it both as a seperate program and as an add-on in my browser (Chrome). You might also want to run a spyware program, I use SuperAntiSpyWare...
I use chrome. I probably need to do a better job of clearing the cache. I will look at adding a cleaner program
Generally speaking, as a rule of thumb, just like car shopping...you should buy the best/latest computer you can afford, But don't buy completely brand new retail...buy used or refurbished on eBay for noticeable savings,
If you are trading you should have a dedicated system with nothing else installed, or be very diligent in what you do install neither of which most follow. Always good to re-install the OS every year or two, I just buy a new computer but that's not really suitable for most.
I think your hard drive is either too full, or more likely just too cluttered. My guess is that you simply need a hard-drive clean-up. Ccleaner, recommended above, would be a good start. You'll probably be amazed at what it finds and removes. Defragmenting the hard drive would also probably help.
When your trading apps are loaded, check Windows Task Manager to see how much RAM is in use. If it's not a high percentage, adding more RAM will not help and you'll have to look elsewhere.
Your problem might just be a fragmented harddrive and a large cache. So when you open a new tab, it's trying to read stuff from cache and can't do it fast enough. It's not your CPU or anything else most likely. 8GB of RAM is plenty for normal use unless you have say 50+ tabs open with heavy graphics. For a new setup: Get an SSD which costs more than HDD at same size but is much much faster on new systems. So if you should have a hardware problem that requires a restart, you can be back trading in less than a minute. With a HDD that's easily 4 minutes. SSD should be the default choice for every system drive, HDDs for things like video editing. If you want a graphics card, get one that stops the fans in 2D use, it'll be very quiet.