Can't get HL2 working

[luckSpray]

Yesterday I've installed HL2 and played to the 4th chapter... today (after sleep, reboot, and HL2 update [forced by Steam]) I can't start HL2... after the Valve-intro, Windows prompts an error message about a memory location which can't be read.

Here's the message (Windows XP Pro ger.):
http://193.171.155.106/~hiroyuki_sakai/DATA/Image2.jpg

I don't think that this is a hardware problem because I haven't done anything terrible against my hardware...

Shall I try to reinstall HL2? Hopefully not (I fear messing up Steam and re-expriencing the long long decryption)

Please help me!

[compucomp]

this is the memory read error, if I'm reading the German correctly. there are many threads devoted to this topic, so you can look at some of those.