Ok when ever i go in to the sewers the computer shuts down on me. can someone tell me why?

what EVERY time u go into the sewers? ok:

1. do u have any plugins running? it could be a conflict so disable and re-enable them one at a time until u stop crashing in the sewers and disable the one that did it.

2. do u have the latest patch? if not get it

3. try reloading an earlier savegame?

4. try re-installing the game

Also check out the threads on CTDs in the technical support forum - maybe you find some useful information there.

Does the game always crash in the same place/situation or does it vary?

It varies.

I have no plug-ins, i have reinstalled, i have the latest patches to.

Now i cant do any missions i wanted to do.

Read the thread I made in the tech forum and clean out your PC.

And be more specific. MUCH MORE SPECIFIC.

Like making a post with at least 30 sentances discribing your problem, what, when, when not, what plugins you use, what OS you use, what hardware you have, and ESPECIALLY which programs you run in the background, since that is crash reason #1.