There are a number of different problems mentioned above, and so possible a number of different underlying problems that all need to be fixed. We'll cover this in order, starting with your machine.
Before we continue you need a copy of SystemRescueCd. Go and download it now while you're reading the rest of this post. Its a Linux based system rescue disk available as a bootable CD-ROM.
Hardware
Looks like you're using decent brand hardware; good start. One thing to check (probably not the cause of your problems, but I'm trying to make this a fairly generic post) is the PSU. Check the wattage is suitable for you system; if its more than a few years old then consider updating it anyway. A poor PSU can result in any number of bizarre problems.
Also I'm going to assume that you've not over-clocked your machine nor flashed your motherboard or videocard with third-party firmware. If so you're on your own.
Memory / CPU
Boot your machine from the SystemRescueCd and select the memory test option; this should start Memtets86+. Let it run for as long as possible, overnight is good. Your looking for a 3+ passes, no errors. If there are any erors then get these fixed (i.e. replace RAM) and repeat this step before continuing.
Harddrive
Next up for testing are your harddrives; we're going to use the built-in firmware tests (SMART) for this. These tests are safe and non-destructive; no data is written to your disks.
Reboot your machine, again using the SystemRescueCd, and select either rescuecd or rescue64 depending on your machine.
We need to find your harddrives; these will be accessed via names of the form /dev/sdX where X is 'a', 'b', 'c', .... . Use the following command to identify your harddrives; this should print out the make, model, serial # (as well as a bunch of other information):
Once you've found your harddrives we need to test them. There are two tests available, short (takes 1-2 minutes) and long (takes 1hr or more. For each harddrive use the following commands:
Enable SMART for a harddrive:
$ smartctl -s on /dev/sdX
Display all SMART information.
$ smartctl -a /dev/sdX
Run the short self-test
$ smartctl -t short /dev/sdX
Run the long self-test
$ smartctl -t long /dev/sdX
Display all SMART information again.
$ smartctl -a /dev/sdX
Hopefully the last command will show that both tests run and completed without error. If the tests are failing you'll want to fix (i.e. replace) the harddrive before repeating this step and continuing.
If you've got multiple harddrives you can use different virtual consoles to run the tests in parallel; hit alt-F1, alt-F2 to swtich between the virtual consoles.
Operating System
Check that all Window updates are installed and all hardware drivers are up-to-date. Also that you've got anti-virus installed and a full scan is clean. There are numerous free anti-virus available, I tend to use Microsoft Security Essentials these days.
Consider also using the free version of MalwareBytes to double check your machine for problems, and CCleaner to clean up any register problems.
Perpetuum
Perpetuum crashing during installation is a common problem and has been reported several times on these forums. Its caused by a race condition in the installer when it tries to update the .exe file. The solution is simple; reboot and try again.
Network
I'm also a UK player, using a cable connection (Virgin Media ), with constent ping times of 150ms and very few disconnects (once / week?). While I don't want to point fingers BT hardly has a stellar reputation.
Couple of suggestions:
Are you using wireless to connect your machine to your router? If so switch to a wired connection.
Buy/beg/borrow a 3G modem (or Android phone) and attempt to play over a 3G connection. Lag times will be slighter greater but this will remove BT from the equation.
While its true that BT owns the local infrastructure there are any number of ISPs with their own backend infrastructure. If you're willing to pay a fraction more I suggest looking at aaisp.net. They run an uncongested network, constantly monitor your connection to quality (and make this information available to you) and more.
Hopefully this helps; any questions ask below.