system secure against user

I have a few problems that i think are connected to some security applications that have possibly configured things such that limitations on the user have become excessive. The account in use is not teh administrator account but has admin privileges.

I had trouble accessing a lot of web sites in Chrome and didn't want to use for general surfing super-secure Firefox [the 'web site not available' problem in Chrome was caused by Peerblock], so downloaded Opera, Seamonkey and Pale Moon. For the first two, attempts to install them result in "This program is blocked by group policy" and for the last, the error is that the installer needs to be run in a writable location or with fewer restrictions. Other things have been installable, such as Hitmanpro and Spybot. Various anti-malware scans have been run.

I've looked in the local security policies and can't see anything in there at all. With the writable location, turning off the Comodo sandbox was something tried without success.

Also wanting to use a small Java-based chat application in a website, and although Java has previously been installed in Chrome it is there no longer in teh plugin list. Scripting of Java applets is enabled in Internet Options. Running the Java Chrome Installer doesn't put it there. Something is preventing Java from installing in Chrome. Could that be a particular Chrome Extension or is this problem likely to have the same cause as the unable-to-install-browsers problem?

If I post a hijackthis log or equivalent, could someone more knowledgeable than me suggest which program it might be that makes the machine so secure that new browsers can't be installed?

 

forgot-
Windows 7 Ultimate (x64) Service Pack 1 (build 7601)
Mainboard Gigabyte P55A-UD3
CPU 2.93 gigahertz Intel Core i7 870 Bus Clock: 133 megahertz
8184 Megabytes Usable Installed Memory
NVIDIA GeForce GT 220 [
3000.49 Gigabytes Usable Hard Drive Capacity