Good trading computer?

As for your other issues, I would say the whine you hear is the cpu getting hot, you say the system shuts down also which may also be a sign of a hot cpu and the fail safe is triggered. (speccy will also let us know the cpu temps). The second issue could be a system fan going bad. But those usually do not make a high pitch that you say bothers you. But in any case you can solve both, if you are up to a little dismantle type work. If you want to go for it and try, we can walk you through it. Not difficult at all really, just need to be careful as you do it. These things would probably resolve the issues you have, if not we would need to look at a possible memory stick failing or even windows degrading as it does over time. Both not hard to fix either. So lets start at the web downloads and go from there.

Now as for the set up you have.. you do have a good unit, a dell workhorse for many years. Based on the cpu I will guess somewhere in the 2007-2008 age range. You have a good dual core processor that will hold its own with many of the newer ones. The system originally was designed for servers and graphic work stations. It ran 4 monitors out of the box with ease. It does sound like that with out much time money and effort the system would still fit your needs.
So the possiblities as I see it are
1. Scrap this and go for a new one.. $1000 price range is achievable
2. Fix this one, unknown dollar amount but I wouldn't go over $500.. new ram and cpu can be found for $100
3. Fix and upgrade this one, Another unknown as it depends on what you have now and limitations of age on upgrading.
4. This is my favorite, do both.. I would fix this one and add a few upgrades. Then I would decide as to what I want and need for the future. Build that over time as money allows. Then you would have a new build and a good reliable back up. This one also tends to piss off the wife or partner.. added benefit. lol

Again the upgrades depend on the board and system components there, some you can do and some will not be possible. The cpu now is dual core and rated at 64 bit, also supports multi monitor. You could set up four screens and spread a chart across all four if you want. The board I am unsure of as they used several, it is a pci board and both the board and cpu max out at 1066 ram speed I believe, but you can easily have 4 gb on the memory or more and compensate for speed that way. . I believe you are also limited to 500mb on vid cards but you can have two. The other question then would be the power supply limits, but that is down the road. As for the operating system the system is rated for vista, win 7 may work but may end up using vista drivers anyway. If the os is changed you would need to get the ultimate or pro versions as they are backward compatible to xp/vista drivers. just another way for ms to get more money.. I did check out Sierra, they don't exactly give you spec rewuirements, but from what I can see all you need is 2 gb ram and a dual core processor so you would be safe there. As for Win 7, it also requires a dual core processor, ( actually not true ) and 2gb ram, I would say at least 4 gb ram up to 8 gb is enough. I don't see any benefit in adding another cpu, at least from what you desribed as your usage.

Ok should be enough to think over, See what Raptor has to add and suggest. Then go from there...