well... pb is hard thing... and it needs freedom thats 4 sure...
i'm encountering this problem almost (: always after some time not playin... or playing w.o. pb... it updates... talking about windows.. hope im not wrong too much...and there many things can block for proper b startup even taht can mean ur hardware problem instability at some levels... like electricity variation with lowcost psu's... etc

*mainly Firewall's (or separate soft's) with Host-based Intrusion Prevention System (HIPS).. that can prevent processes, windowsRegistry; INI-files; from loading proper drivers/dlls/services, starting them at all ...so check your logs

*firewalls with md5.. hasch based file identifiers..if rules was set for pb's exe's after some updates they have new, so rules must be recreated or renewed(if soft not suports automatic recalculation or something..); +be sure too allow, well, all to those trycky pb's (; ; some soft even can do not warn if they have already created rule for that patch ...

*hmn im not sure but it's posible that PnkBstrB.exe can be corupted somehowe (: or something, if it fails to start.. then just delete %\WINDOWS\System32\PnkBstrB.exe
pb will replace it; worked couple times for me, i even suggesting try fiirst this (make backup; i don't know if it important ..my pb's autoupdate works, have no probs)

couple examples from my fw.. old and new have diferent hash's
App Trusted Zone disabled any<cut>any F:\WINDOWS\System32\PnkBstrB.exe
Hash 7C7B0105 7707C223 4FF3F1F2 A84DCFB4 6B295B37 -date070708

app accept disabled any<cut>access F:\WINDOWS\System32\PnkBstrB.exe
Hash AA8F37BF CA4C6260 68A9B9AB C851C30A 42423D92 -date071208

registry inspected changes/strings.. arent important.. if some registry aka protectors or something, dont dissallow some zones from changes..(in example isnt exact values-only notifys)
and notice.. pb creates temporary PnkBstrK procces.. maybe some stuff can prevent this proces from starting other pb's stuff (it seems PnkBstrB ..dont care to m. see below):
Services:\\PnkBstrK Remove PnkBstrK Running 2007.12.12 10:41:51
Services:\\PnkBstrB Remove PnkBstrB Running (Automatic) 2007.12.12 10:41:51
Services:\\PnkBstrK Add PnkBstrK Running 2007.12.12 04:10:37
Services:\\PnkBstrK Add PnkBstrK Running 2007.12.12 02:31:51
Services:\\PnkBstrK Remove PnkBstrK Running 2007.12.12 01:59:53
Services:\\PnkBstrB Remove PnkBstrB Running (Automatic) 2007.12.12 01:59:53

chill time 4 Electronic lovers get this (: Autechre - [Basscadet (EP) #02] Beaumonthannanttwomx [1994]