This used to happen to me in BFBC2. It sucks, and it will be gone between an hour or a few days. You will probably get your stuff back eventually, if not, you're screwed.
well the sg 553 is a gun you unlock on co-op mode, you get all the guns from online mode by leveling up, theres more in the map pack "back to karkrand" and soon to be "close quarters" as for co-op mode you recieve guns such as the mp7 kh2002 , m39 93r etc
Here are all of the infintry wepons: Assalt: M320, M416, M26, AEK-971, M16A4, F2000, AN-94, AK-74M, KH2002, G3A3, AUG A3, SCAR-L, FAMAS, L85A2. Engineer: Rockets, Mine, SCAR-H, M4, A-91, G36C, AKS-74u, M4A1, SG553, ACW-R, MTAR-21, G53, QBZ-95B. Support: Claymore, Mortar, C4, M249, PKP PECHENEG, M240B, M60E4, M27 IAR, RPK-74M, L86A2, LSAT, QBB-95, MG36, TYPE 88 LMG. Recon: SV98, M4OA5, M98B, MK11 MOD O, SVD, M39 EMR, M417, JNG-90, QBU-88, L96, SKS. Misc: MP7, 870MCS, PP2000, UMP-45, M1014, PDW-R, SIAGA 12K, P90, USAS-12, AS VAL, SPAS-12, M5K, PP-19, MK3A1, KNIFE, ACB-90, DAO-12. Pistol: MP412 REX, 93R, G17C, M9, MP443, G18, .44 MAGNUM, M1911. This is all of the guns I know of as of 6/14/12 (Including Close Quarters and Back to Karkand). I haven't included anything that isn't spacificly designed as a wepon (like the defibulators which can kill but are designed for reviving)